Firefighters in Southern California were working to contain a quickly growing wildfire in Ventura County on Thursday afternoon, prompting thousands of residents to be ordered to evacuate the area.

The blaze, called the Canyon Fire, began early Thursday afternoon near Lake Piru, a reservoir about 60 miles northwest of downtown Los Angeles. The fire was initially reported at about 30 acres, but within a few hours it had rapidly grown to consume an estimated 1,050 acres, a spokesman for the Ventura County Fire Department said.

The Canyon Fire was burning on a particularly hot day in Southern California, with a high temperature expected to reach nearly 100 degrees in the area of the fire and dry conditions that could help fuel the flames even more, according to the National Weather Service.

More than 16,000 residents were under evacuation orders or were being told to prepare to evacuate, based on a New York Times analysis of the evacuation zones and LandScan population data.

Andrew Dowd, the spokesman with the Ventura County Fire Department, said an estimated 150 to 200 firefighters were on the scene.

“We’re doing a significant initial attack,” Mr. Dowd said.

This is a developing story and will be updated.