Two fires about 100 miles (161 kilometres) north of San Francisco are just 30 percent contained as of Tuesday, fire officials said.
So far, the growing blazes have scorched 428 square miles (1,108 square kilometres) and have destroyed 75 homes.
Another 9,000 buildings are threatened by the fires, which burn just 14 miles apart.
The two fires now cover an area larger than a deadly wildfire burning near Redding, California.
The Army is drafting in 200 active-duty soldiers and emergency fire crews to help battle the raging wildfires in the Western USA.
Soldiers from Joint Base Lewis-McChord, Washington, will get three days of training starting on Thursday and will all be deployed to the same fire.
Here is the latest news and live updates on the California fires.
10pm update: What happens if firefighters can’t put out the blaze?
Evacuations have been put in place across California, as the fires are showing no signs of slowing down.
Strong winds are also not helping as they are fanning the flames even more.
Firefighters are using water and extinguishers where they can.
But if that approach does not work, they will head to a ridge, wide road or stream where they will then use bulldozers to cut a “fire line.”
8.52pm update: When will the wildfires be put out?
Only 30 per cent of the Mendocino fire is contained so far.
Authorities have warned it could take another week to get the blaze under control.
The fires are believed to have started due to scorching temperatures.
Some areas of California have been forecast highs of at least 43C (110F).
National Weather Service meteorologist Brian Hurley has said conditions are not going to improve any time soon.
7pm update: What has happened so far?
To recap, the twin wildfires in California, known as the Mendocino Complex Fire, have become the largest active wildfire in state history.
The fires have burned more than 283,800 acres of land, which is equivalent to an area alomst the same size as the city of Los Angeles.
Scott McLean, deputy chief of the California Department of Forestry and Fire Protection (CalFire) described the wildfires as: “extremely fast, extremely aggressive, extremely dangerous.
“Look how big it got, just in a matter of days… Look how fast this Mendocino Complex went up in ranking. That doesn’t happen. That just doesn’t happen.”
5.37pm update: The fires can be seen from outer space
Images obtained from NASA show the Carr fire on July 27 and also the Ferguson fire on July 29.
The wildfires have now burned through 283,800 acres (114,850 hectares).
This is nearly the equivalent size of the city of Los Angeles.
The fires remain 30 per cent contained, according to state fire authority CalFire.
The fires in California can be seen from space
NASA’s Terra satellite captured the fires when it passed over California last week
3.37pm update: The fires are costing millions of dollars to put out
The US Forest Service has revealed it is remaining at national wildfire preparedness level 5, which is the highest possible.
More than 27,500 USDA Forest Service firefighters are currently tackling different wildfires around the US.
The Carr fire is covering more than 160,000 acres and is 43 per cent contained.
The costs of this fire have now exceeded $ 60 million.
The Ferguson fire is covering nearly 90,000 acres and is 38 per cent contained.
Both Sierra National Forest and Stanislaus National Forest are affected now too.
2.50pm update: The UK Foreign and Commonwealth Office (FCO) latest travel advice to California
The UK Foreign and Commonwealth Office (FCO) explains their latest travel advice to California on their website.
“Wildfires can spread swiftly, so if you’re in the area you should remain vigilant, monitor local media reports, and follow the instructions issued by local authorities, including obeying any evacuation orders,” the FCO advises.
If you’ve been affected by the wildfire and need consular assistance, you can call the British Consulate in San Francisco on +1 415 617 1300; if you’re in the UK and worried about a British national visiting the Yosemite region, you can call the FCO on 020 7008 1500.
2.39pm update: More than 11,000 structures still threatened in Mendocino Complex fire
The Mendocino Complex fire is burning in mostly rural areas, but 143 buildings have been destroyed, including 75 homes, and 26 other buildings have been damaged.
Another 11,300 structures remain threatened, according to Cal Fire.
There have been no deaths associated with the Mendocino Complex Fire.
2.00pm update: The Ferguson Fire is now the largest fire in the Sierra National Forest’s History, with two fatalities and 11 injuries to date.
Since the Ferguson Fire began on Friday, July 13, 2018 park visitors, employees, local businesses and communities have all been affected.
CalFire’s Sunday afternoon report said: “Over the past 48 hours, fire has impacted all of the roads used to access Yosemite Valley, burning dead and downed trees that can become very explosive and fall without warning.”
California fires: Emergency firefighters drafted in
12.17pm update: The worst is yet to come, warns California governor
Cal Fire director Ken Pimlott said on Saturday: “Fire season is really just beginning.
“What seems like we should be in the peak of fire season, historically, is really now the kind of conditions we’re seeing really at the beginning.
While California governor Jerry Brown warned the worst was yet to come, as fire season has only really just kicked off.
He said: “We don’t like to scare people. I only wanted to say we’ve got tough times ahead and no matter how comfortable you feel or how everything looks good, the part of wisdom is to be ready for what we don’t know.”
12.00pm update: Fire crews are determined to stop the lazes from destroying even more land
Jeff Harrison, a firefighter tackling the fires told ABC: “We’re mobile. We’re self-sufficient. We have MRE’s meals ready to eat on the engine.
“It’s just part of the firefighting game, to be prepared and live off of little sleep.”
He added: “Not only do we have to have our head on a swivel for fire, we also have to be very cautious about possible trees that are going to fall, because if they fall, they kill.”
10.52am update: New California fires map shows where homes are most at risk
Two million homes are at risk of being burned to the ground, according to analysis from Verisk Analytics.
The map graphic shows the locations most vulnerable to wildfires just like the Mendocino Complex fire which has already burned through hundreds of thousands of acres.
A total of 15 percent of all homes in California are under threat, with northern areas most at risk.
California fires map: Two million homes are at risk of deadly blazes
10.38am update: Yosemite Valley National Park is still closed to visitors
Within the park, the Ferguson Fire is “dynamic,” CalFire’s Sunday afternoon report said.
So far, the fire has burned 140 square miles (89,633 acres) and is 38 percent contained.
Full containment is estimated by August 15 – but weather conditions could help fan the flames further, some warned.
The Cal Fire report read: “Over the past 48 hours, fire has impacted all of the roads used to access Yosemite Valley, burning dead and downed trees that can become very explosive and fall without warning.”
10.00am update: Hot and windy conditions are proving a challenge for fire crews battling eight major blazes burning out of control
No one has been injured in the Mendocino Complex Fire, which consists of the Ranch Fire and the River Fire, burning around Clear Lake in several counties in Northern California.
Another major fire also burning in Northern California, the Ferguson Fire, extended into its third week.
The Carr fire is now covering 164,413 acres and is 47 percent contained, while 95 percent of the Whaleback fire is now under control.
Yosemite fire map: Yosemite Park has closed after 140 square miles is ravaged by flames
9.25am update: Authorities have evacuated cabins in two communities in the Santa Ana Mountains
Jeanna Smith, from the US Forest Service, says firefighters are attacking the fast-moving Holy Fire in Orange County with a DC-10 air tanker and helicopters.
Crews are “hitting it hard with everything we’ve got”, she said, as officials try to halt the fire at the top of a ridge – keeping it from homes just a couple miles away.
The fire began around 2 pm Monday and quickly grew to more than a square mile (2.6 square kilometres).
9.00am update: Temperatures to soar – fanning the flames even more
Temperatures could reach 43C (110F) in Northern California over the next few days.
Gusty winds will also help to fan the flames of the complex, a National Weather Service meteorologist said.
“Rapidly-rising air caused by the extreme heat helps the fire to grow explosively as the fire will create its own wind, as well as fire vortices (firenadoes) and tree crowning (when the leaves get engulfed by flames), even on otherwise calm days,” AccuWeather Meteorologist and volunteer firefighter Evan Duffey said.
The 3,900 crews battling the Mendocino Complex on Monday were focusing on keeping flames from breaking through fire lines on a ridge above the foothill communities of Nice, Lucerne, Glen Haven, and Clearlake Oaks, a spokeswoman for Cal Fire said.
California fires map: Wildfires show comparison of largest blazes
California fires map: Fires have spread to more hundreds of thousands of acres
8.50am update: US President Donald Trump declares a “major disaster” in the state
“California wildfires are being magnified and made so much worse by the bad environmental laws which aren’t allowing a massive amount of readily available water to be properly utilized,” Trump wrote on Twitter.
A California Department of Forestry and Fire Protection spokesman declined to comment on Trump’s tweet.
However, the official rebuffed the President’s suggestion that fire crews lacked water to fight the flames.
Environmental activists and some politicians say the intensity of this year’s wildfire season could be linked in part to climate change.- a phenomenon Donald Trump denies.
8.39am update: Mendocino Complex fire now the largest in history
The Mendocino Complex became the largest wildfire in history on Monday after the blaze grew to 283,800 acres (114,800 hectares) – and is still spreading.
The fire is currently raging at the southern tip of the Mendocino National Forest, where crews are battling to keep flames from descending into foothill communities.
The fire has now surpassed the Thomas Fire, which burned 281,893 acres in Santa Barbara and Ventura counties in 2017.
And as prime weather conditions are expected to persist, the blaze is expected to grow even bigger.
“Unfortunately, they’re not going to get a break anytime soon,” National Weather Service meteorologist Brian Hurley said of firefighters who had cut buffer lines around 30 percent of the blaze.
“It’s pretty doggone hot and dry, and it’s going to stay that way.”