(Reuters) - Firefighters in Southern California were battling a fast-moving wildfire on Sunday that closed a highway and forced residents from their homes around the area of Santa Clarita, a city north of Los Angeles, authorities said.

The fire broke out in the early afternoon after a traffic collision caused a tree to catch fire, the Los Angeles County Sheriff’s Department said in a statement.

The blaze swelled to roughly 800 acres (324 hectares) but firefighters had managed to contains about half the blaze by 6 p.m.(0100 GMT), the Los Angeles County Fire Department tweeted. Its size at that point had shrunk by about 50 acres, the department said.

An image posted by fire officials on Twitter showed two massive plumes of smoke swirling toward the sky over a blackened hilly landscape in the foothills of the San Gabriel Mountains.

The blaze was burning in the southeastern area of Santa Clarita, a city of some 181,500 residents.

Authorities issued mandatory evacuation orders for residents in some areas threatened by the blaze, though it was not clear how many people were affected, the Los Angeles County Sheriff’s Department said.

One structure was destroyed by the fire and State Route 14 was closed in both directions earlier on Sunday, but traffic has since resumed, the department said.