A cooking fire at a homeless camp ignited the wildfire that threatened the affluent Los Angeles neighbourhood of Bel Air, officials have said.

“Investigators have determined the fire was caused by an illegal cooking fire at an encampment in a brush area adjacent,” the Los Angeles Fire Department said in a statement, adding that no arrests had yet been made in connection with the fire.

While not as large as the two other blazes that scorched thousands of acres in Los Angeles County, the Skirball Fire attracted attention as it imperilled upscale homes and the Getty Center, feeding on dry brush in the hills.

After roaring to life on Wednesday morning, the blaze consumed hundreds of acres, incinerated six structures and damaged a dozen others. Los Angeles residents shared apocalyptic images of hills cupping the city engulfed in flames.

Firefighters had the fire 85 percent contained as of Monday evening, and residents who earlier faced mandatory evacuations had begun returning to their homes days earlier.

Two fires that had collectively burned across thousands of acres in northern Los Angeles County were also largely under control, as was a conflagration that had roasted some 4,100 acres in San Diego County.

The 'Skirball Fire' takes hold in LA Show all 11 1 /11 The 'Skirball Fire' takes hold in LA The 'Skirball Fire' takes hold in LA A member of a fire team hand crew monitors embers to prevent fire from jumping to the west side of the 405 freeway, at the Skirball Fire near the Bel Air area of Los Angeles, California, December 6, 2017. AFP/Getty Images The 'Skirball Fire' takes hold in LA A house is threatened by wildfire along Linda Flora Drive during the Skirball Fire in Los Angeles, California, December 6, 2017. The "Skirball" fire ignited before 5 a.m. (1300 GMT) and quickly engulfed some 50 acres, with forecasters predicting the 25-mile-per-hour winds could cause further spreading, threatening multi-million dollar homes and the acclaimed Getty Center museum. AFP/Getty Images The 'Skirball Fire' takes hold in LA Firefighters work to save burning houses along Linda Flora Drive during the Skirball Fire in Los Angeles, California, December 6, 2017. AFP/Getty Images The 'Skirball Fire' takes hold in LA Flames from the Skirball Fire spread on a hillside in a wealthy neighborhood on the west side of Los Angeles, California, U.S., December 6, 2017 REUTERS The 'Skirball Fire' takes hold in LA Brent Thomas of Cassiano Road waits for a police escort to take him back to his evacuated home on Cassiano Road in the Bel Air district of Los Angeles, CA in order to pick up medication. Brent has no idea when he can return home after being evacuated due to wild fires this morning. Ruth Iorio The 'Skirball Fire' takes hold in LA Firefighters stop for a quick bathroom break on Moraga Drive and Sepulveda, close to the Getty Center in Los Angeles, CA, at around 4pm on Wednesday December 6 2017, after fighting the wild fires in Sylmar and Bel Air for over thirty hours. Ruth Iorio The 'Skirball Fire' takes hold in LA Smoke from the Skirball Fire rises above the 405 freeway near the Bel Aire area of Los Angeles, California, December 6, 2017. AFP/Getty Images The 'Skirball Fire' takes hold in LA LAFD Firefighter Allen Janzen puts down smoldering embers in the Bel-Air section of west Los Angeles, California to protect home against the Skirball Fire, December 6, 2017. AFP/Getty Images The 'Skirball Fire' takes hold in LA Firefighters work to save burning houses along Linda Flora Drive during the Skirball Fire in Los Angeles, California, December 6, 2017. AFP/Getty Images The 'Skirball Fire' takes hold in LA A firefighter works to save burning houses along Linda Flora Drive during the Skirball Fire in Los Angeles, California, December 6, 2017. AFP/Getty Images The 'Skirball Fire' takes hold in LA A home burns as a wildfire dubbed the Skirball Fire moves through a wealthy neighborhood on the west side of Los Angeles, California, U.S., December 6, 2017. REUTERS

But the massive Thomas Fire continued to burn across a wide swathe of Ventura County and Santa Barbara County, where thousands of people have been forced from their homes and nearly 800 structures have crumbled in the flames. Flames have consumed some 234,000 acres.

In its latest update, Cal Fire warned that “severe fire weather” conditions of gusty Santa Ana winds, low humidity and parched vegetation would continue to feed the inferno and create obstacles for firefighters struggling to curb it.