Los Angeles firefighters remained on arson alert Sunday after theHollywood district celebrated the New Year under the cloud of a string of some 40 deliberately-set fires.

Seven new fires were reported overnight, including one in an underground parking lot near the heart of Tinsel Town's tourist district, the LA Fire Department (LAFD) said.

Amateur video published by the LA Times newspaper caught the blaze in the basement of the Hollywood and Highland center, near Grauman's Chinese Theatre, where tourists flock to see celebrity handprints and the Walk of Fame stars.

The LAFD had put fire crews on alert for more arson attacks on what is traditionally a busy night anyway, as Angelenos usher in the New Year.

Federal investigators have been called in to help the LA Police Department (LAPD) and LAFD probe the string of arson attacks, one of the worst sprees in the city since the 1992 race riots.

No new arrests were made overnight, according to officials speaking at an early Sunday morning press conference.

"I'm not going to speak anything about the type of devices" used, said LAFD assistant chief Pat Butler. "We do believe we have incendiary, intentional fires that result in auto fires that result in apartment fires."

The LAPD's Major Crimes and Robbery-Homicide divisions were analyzing security video camera pictures.

"We've reassigned dozens of detectives," said LAPD commander Andrew Smith. "Those detectives are now working together around the clock.... We've got hundreds of clues, dozens of witnesses, and countless pieces of evidence."

More than 30 fires were started overnight Thursday and Friday, mostly targeting cars either outside homes on in car ports under buildings, which then caught alight. No serious injuries have so far been reported.

The new attacks on New Year's Eve and early Sunday included two in West Hollywood and five in the city of Los Angeles, while another was reported in Burbank on Saturday, bringing the three-day total to around 40 blazes.

Damaged property included a Hollywood Hills home where singer Jim Morrison of The Doors -- whose hits include "Light My Fire" -- once lived, and where he wrote the legendary band's "Love Street."

At least two people are under arrest, according to media reports, including a 22-year-old man charged with starting three fires on Thursday. But they were behind bars overnight Friday and Saturday when new blazes were set.

City and county officials, along with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (BATF), have posted a reward of $60,000 for information leading to the arrest of those responsible.