Los Angeles (CNN) -- A joint task force Saturday was investigating a string of 35 fires across several Southern California communities, and one mayor called them a "new form of domestic terrorism."
Despite a $60,000 reward, authorities had not made an arrest by Saturday afternoon.
The 21 initial fires, set in rapid succession in the Hollywood area, prompted authorities in California to post the reward in what they say is one of the worst arson sprees in recent memory.
The fires were set within a span of about five hours early Friday morning, and in nearly every case they were started on parked cars, officials said. Some of the fires spread to nearby buildings.
Among the homes damaged was one that was once occupied by Doors frontman Jim Morrison. The street where the house sits -- Rothdell Trail -- was the inspiration for the Doors song, "Love Street."
Seventeen fires were set in Hollywood; four others in West Hollywood -- all of them within a 2-square mile area.
The fire department's Capt. Jaime Moore told CNN Saturday an additional 14 fires were reported. Investigators will determine whether they are arson and related to the other fires.
"This area of concern involves vehicle fires and fires involving vehicles in structures," the Los Angeles Fire Department said in a statement. "Ten of these fires were located in the North Hollywood (Burbank) area and the last three were located in the Fairfax district (southwest of Hollywood). The Los Angeles County Fire Department has reported one fire meeting this criteria in the Lennox area."
West Hollywood Mayor John J. Duran told CNN the arsonists "are using cars as an incendiary device to set buildings on fire." Many of the buildings are close to each other and house senior citizens who are not mobile, he said.
"We have a full-force deployment out tonight," Duran said.
"When you have millions of people living with millions of cars in these very dense neighborhoods, this is becoming a new form of domestic terrorism that really has got our community in a very bad spot."
County Supervisor Zev Yaroslavsky told reporters Friday afternoon that authorities are "dead serious about trying to apprehend the individual or individuals who are responsible" for the arson fires.
"We want to get these SOBs before they hurt somebody," he said.
Fire officials said they were relieved no one was hurt, although a firefighter suffered a non-life-threatening injury.
"If you're setting something alight when people are going to bed, you obviously don't expect them to wake up," resident Mark Todd told CNN affiliate KTLA. "It sort of goes past arson to attempted murder."
The Hollywood area is home to about 20,000 people per square mile, said Los Angeles fire spokesman Erik Scott.
He also said the fires caused $350,000 in property damage -- a "conservative estimate."
Authorities deployed extra police officers after sundown. The Los Angeles Fire Department's arson unit called in additional investigators to review surveillance footage and pore through the ashes.
"While our police officers and our fire departments are working on high alert in coming days, everyone must remain vigilant," said Los Angeles Mayor Antonio Villaraigosa.
CNN's Adam Shivers contributed to this report.