Utility company Southern California Edison (SCE) said its equipment is under investigation as a possible source of a blaze that erupted early Monday and spread across 7,200 acres of California's Orange County by late afternoon.

About 90,800 residents were ordered to evacuate from their homes in and around the city of Irvine as the so-called Silverado Fire raged largely unchecked through drought-parched brush in the canyons and foothills of the Santa Ana Mountains south of Los Angeles, officials said.

No property losses were immediately reported but two firefighters were hospitalized with severe burns.

Two firefighters, one 26 and the other 31 years old, were critically injured while battling the blaze, according to the county's fire authority. They each suffered second- and third-degree burns over large portions of their bodies and were intubated at a hospital, officials said.

Southern California Edison submitted an initial electric safety incident report to the California Public Utilities Commission on Monday, a spokesman said.

"It appears that a lashing wire attached to a telecommunications line may have contacted SCE's power line above it, possibly starting the fire," he said.

The cause of the fire will be probed by the Orange County Fire Authority, the spokesman said, adding SCE will cooperate with the investigation.

The report came as SCE shut off power to some 38,000 homes and businesses in five counties – including the fire areas – as a safety precaution against gusts knocking down equipment or hurling tree branches or other vegetation into power lines. 

However, the utility had reduced that to under 16,500 as winds eased temporarily Monday night.

The latest threats came amid what meteorologists called the strongest onslaught of extreme winds – and lowest humidity levels – yet documented during an already epic California wildfire season ranked as the worst on record in terms of acreage burned.

Fires have scorched more than 6,400 square miles (16,500 square kilometers), with thousands of homes destroyed and 31 lives lost. Red flag warnings for incendiary weather conditions remained in place across much of California.

(With input from agencies)