A pair of wildfires has destroyed dozens of homes near Los Angeles, killed a man, and 100,000 residents have been ordered to evacuate, fire officials said on Friday.

It came days after power cuts were ordered across California to prevent fires.

In the San Fernando Valley north of Los Angeles, the so-called Saddleridge fire had spread to more than 4,700 acres by Friday morning, moving at a rate of 800 acres per hour, the Los Angeles Fire Department said. It is still completely uncontained.

Officials said one man died from a heart attack, which they attributed to the Saddleridge Fire. The cause of the fire is under investigation.

Some 23,000 homes and some 100,000 residents were under mandatory evacuation orders on Friday morning and should not expect the orders to be lifted for at least a few days, department officials said.

"This is a very dynamic fire," Los Angeles Fire Chief Ralph Terrazas said. "Do not wait to leave."