A man who dressed as Santa Claus to kill nine Christmas Eve party guests before taking his own life had been divorced just a week when he unleashed a hail of gunfire and flames that seemed intended for his former wife and in-laws, officials said.

Authorities in the suburban town of Covina, 37 km northwest of downtown Los Angeles, still were trying to comprehend what drove Bruce Jeffrey Pardo, 45, a jobless engineer and longtime church usher, to carry out his fiery rampage.

But survivors told police Pardo seemed to zero in on his ex-spouse and her relatives after he burst into her parents' home at about 11:30 p.m. on Wednesday night, opening fire with four handguns on about 25 party guests there.

"It appears he did have some intended targets, those being family members in the immediate family of his ex-wife," Covina Police Chief Kim Raney told reporters at a news conference.

After running out of bullets, Pardo used a makeshift gas dispenser to spray the inside of the home with a combustible vapor consisting partly of auto-racing fuel, which quickly ignited in an explosion, gutting the dwelling, police said.

The bodies of nine victims, charred beyond recognition, were recovered from the house. Pardo's ex-wife, Sylvia Ortega, 43, and her parents were believed to be among the dead.

Ed Winter, assistant chief coroner for Los Angeles County, said medical and dental records would be needed to identify the bodies, and autopsies to determine whether victims died in the gunfire or the explosion and fire that followed.

Pardo himself suffered third-degree burns in the blast, which melted the Santa suit onto his body. He then fled to his brother's house about 65 km away, where authorities later found him dead from a gunshot wound to the head.

Some $17,000 in cash and airline tickets for a Thursday flight from Los Angeles to Canada were found on his body.

"All indications are that he intended to commit this crime and then flee the country," Raney said. "It appears ... he didn't anticipate injuring himself to the point where he obviously took his own life."

According to a copy of Pardo's resume and other information obtained by detectives, Pardo held degrees in electrical engineering and had worked for about nine years at NASA's Jet Propulsion Laboratory in Pasadena, ending in 1994.

Raney said Pardo lost his job at a radar company in October and that he and his former wife had finalised their divorce last Thursday in a proceeding the police chief described as "somewhat contentious." They had no children together.

A member of Pardo's Roman Catholic congregation in the community of Montrose, 21 km north of downtown Los Angeles, told a newspaper that Pardo had been an usher for the past five or six years and was "just the nicest guy. He would do anything for the church."

Among those who survived the rampage were an 8-year-old girl who was shot in the face by Pardo when she opened the door for him, and a 16-year-old girl who was shot in the back as guests fled in horror.

The house was engulfed in flames when police arrived, about three minutes after someone made an emergency call. One girl jumped from a second-floor window to escape, Raney said.

In a final act of destruction encountered by authorities after Pardo had killed himself, his rental car was discovered to have been booby-trapped with the remnants of the Santa suit rigged to a homemade fire bomb.

The bomb ignited when authorities tried to defuse it, engulfing the car in flames, but no one was hurt, Raney said.

At Pardo's home, police found a supply of racing fuel, empty handgun boxes and two high-powered shotguns, Raney said.