Collectively dubbed the Mendocino Complex, the wildfires have burned through 283,800 acres (114,850 hectares) -- an area nearly the size of the sprawling city of Los Angeles -- and are just 30 percent contained, according to state fire authority CalFire.
Two people have died in the inferno, taking to 11 the number of people killed by major fires that broke out last month and are still ongoing.
"Today a higher pressure system brought warmer weather, drying, and strong winds to the region," CalFire said in an update.
"Tonight fire crews will try to ... increase suppression and hold current containment lines."
It was the second fire to break records in the fire-prone, most populous US state in as many years, following the Thomas Fire in December 2017, which destroyed 281,893 acres.
Further north in the state, the deadly Carr Fire has burned through more than 164,400 acres since July 23, and killed another seven people along the way.
Its intensity was so great at one point, that it generated a tornado-like fire storm -- as well as its own weather system.
Authorities say it was triggered by the "mechanical failure of a vehicle" that caused sparks to fly in tinderbox-dry conditions.
The fire has razed more than 1,600 buildings, including some 1,000 homes, state officials say.
- Fires 'extremely dangerous' -
More than 14,000 firefighters were battling the blazes across the state.
Several thousand people have been evacuated, although some have been given permission in recent days to return to their homes.
The wildfires are "extremely fast, extremely aggressive, extremely dangerous," said Scott McLean, a deputy chief with the California Department of Forestry and Fire Protection.
"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."
The objective of the firefighters is to protect surrounding communities, which have been evacuated. Some 9,300 structures are threatened by fire, while 75 homes have already been destroyed.
"Evacuations are going to continue until is safe" Sheriff Brian Martin said Sunday, without specifying the number of people who had left their homes.
Another major fire, Ferguson, has left two dead and forced the closure of part of the Yosemite national park, and is currently only 38 percent contained.
The weather forecast for the week ahead is not encouraging: very hot and very dry, the perfect conditions for the fires to expand.
The Pentagon announced on Monday it would send 200 soldiers to help firefighters to fight the fires, many of which reached federal lands.
- Trump tweet raises eyebrows -
President Donald Trump raised eyebrows by tweeting about the wildfires inaccurately, claiming there was not enough water to fight them and appearing to place the blame on environmental laws, not climate change.
"California wildfires are being magnified & made so much worse by the bad environmental laws which aren't allowing massive amounts of readily available water to be properly utilized," Trump said.
"It is being diverted into the Pacific Ocean. Must also tree clear to stop fire from spreading!"
"We have plenty of water to fight these wildfires, but let's be clear: It's our changing climate that is leading to more severe and destructive fires," Daniel Berlant, CalFire assistant deputy director, told The New York Times.