By Laila Kearney

(Reuters) - Firefighters struggled on Sunday to contain a fast-spreading wildfire that has killed at least one person, destroyed 18 homes and forced hundreds of evacuations in the drought-stricken canyons north of Los Angeles, officials said.

The so-called Sand Fire grew overnight to 22,000 acres (8,900 hectares), or more than 34 square miles, fueled by high winds and parched conditions after years of drought.

It is threatening a string of small communities near Santa Clarita, just outside the sprawling Angeles National Forest, the Los Angeles County Sheriff's Department said in a statement.

First reported on Friday afternoon, the blaze has forced at least 1,500 residents to evacuate their homes and at least 18 homes have been destroyed, the Los Angeles County Fire Department said in a statement.

All of the affected communities, about 40 miles (65 km) northwest of downtown Los Angeles, are in or around the rugged San Gabriel Mountains. The area is dotted with multimillion-dollar homes.

Some 100 commercial buildings in the path of the fire are under mandatory evacuation orders, fire officials said.

The blaze has belched acrid smoke across a widespread area of Southern California, prompting air quality warnings.

The remains of an unidentified person were found late on Saturday inside a charred vehicle in the path of the blaze. The exact cause of death had not been immediately determined, fire officials said.

They added that they expected extreme heat, strong winds and parched rugged terrain to continue to hamper the efforts of the more than 1,600 firefighters battling the blaze.

The wildfire was only 10 percent contained on Sunday and the cause of was still under investigation.

“This is the fifth year of an ongoing drought, so we have very extreme fire behavior,” Los Angeles County Fire Department Chief Daryl Osby said at a news conference on Sunday afternoon. “These are not normal times.”

Officials implored residents of the affected areas to immediately heed evacuation orders.

“We don’t want to lose any more lives than we did yesterday,” Los Angeles County Supervisor Michael Antonovich told the news conference.

(Reporting by Laila Kearney; Writing and editing by Tom Brown)