Ferocious fires tore through Southern California on Tuesday, burning massive stretches of land in a matter of hours and forcing tens of thousands of people from their homes.

As firefighters in Ventura County grappled with an explosive blaze northwest of downtown Los Angeles, others across the region confronted additional fires that burned during the day and forced additional evacuations. Authorities issued ominous warnings of more dangers to come during a ‘‘multiday event’’ across the area, as weather forecasters said the region faces ‘‘extreme fire danger’’ through at least Thursday due to intense Santa Ana winds and low humidity that could cause the fires to grow rapidly.

The wildfires are the latest grim chapter in a brutal year for California, coming just months after deadly blazes in the state’s wine country killed dozens of people and razed thousands of buildings.

The biggest fire Tuesday was in Ventura County, where a small blaze quickly went out of control as it spread across more than 50,000 acres by the afternoon. The blaze — which burned an area nearly as large as Seattle — stretched into the city of Ventura, home to more than 100,000 people.

‘‘The prospects for containment are not good,’’ Ventura County Fire Chief Mark Lorenzen said at a news briefing as the fire was beginning its aggressive expansion. ‘‘Really, Mother Nature’s going to decide when we have the ability to put it out.’’

As the flames continued to spread, the sun rose over Ventura and revealed the damage left behind by what is named the Thomas Fire. Homes were destroyed and the charred remains of cars sat among heaps of ash. The impact hit home for many of those responding to the blaze: One local fire official told a reporter that he had to call his daughter to tell her that her apartment had burned.

California Governor Jerry Brown declared a state of emergency in Ventura County.

‘‘This fire is very dangerous and spreading rapidly, but we’ll continue to attack it with all we’ve got,’’ Brown said in a statement. ‘‘It’s critical residents stay ready and evacuate immediately if told to do so.’’

What caused the fire remained unknown Tuesday, Lorenzen said. The fire’s ultimate impact also remained unclear. Authorities said at least 150 structures in Ventura County were destroyed by Tuesday afternoon, but Lorenzen said that number could increase in coming days because firefighters were not able to assess the damage in most affected areas. He also warned that there is ‘‘a high possibility’’ that more areas will be evacuated.

Lorenzen said 27,000 people were evacuated, and ‘‘almost none of them know the status of their homes.’’

Some of those who did were given bad news. Debbie Gennaro, who wiped tears from her eyes as she was consoled by her husband, Mark, said they were told that their home of 12 years has been burned to an ashy husk.

They packed up clothes, photographs, and passports on Monday night and headed to a hotel; the couple is unsure where they will go next.

‘‘This is life in Southern California. This is where we live,’’ Mark said. ‘‘I stand on that back hill and I see all that brush and I’m like, ‘Something’s going to happen at some point.’ ‘‘

People who escaped the fires reported apocalyptic scenes. Gena Aguayo, 53, of Ventura, said she saw fire ‘‘coming down the mountain.’’ When Lorena Lara evacuated with her children on Tuesday morning after initially staying put, she said the wind was so strong it was blowing ashes into her home.

‘‘I’ve never experienced something like that,’’ Lara, 42, said. ‘‘Maybe in Santa Barbara, but we didn’t expect it here.’’

Fire officials offered blunt words. ‘‘The fire is still out of control and structures continue to be threatened throughout the fire area,’’ officials in Ventura County said in an update posted online. ‘‘Due to the intensity of the fire, crews are having trouble making access and there are multiple reports of structures on fire.’’

Further east, firefighters also hurried to respond to a wildfire that erupted north of downtown Los Angeles and also expanded quickly, growing to 11,000 acres by early Tuesday afternoon.