Los Angeles: The dramatic Sunday blaze that destroyed portions of Universal Studios back lot was accidentally started in pre-dawn hours by company employees doing roof work with a blow torch, authorities said.

Los Angeles county fire officials said two workers and a supervisor were using the torch to heat roofing shingles on the "New York Alley" set. They finished at 3am (2pm, Dubai), watched for any fire starts for an hour and then took a break. At 4.43am, the same time the crew returned, a security guard spotted flames and reported the fire.

The studio's theme park and adjacent City Walk reopened Monday as the Los Angeles County Fire Department launched what County Fire Chief P. Michael Freeman promised would be a "stem to stern" examination of the water pressure problems that hampered the three-alarm attack on the blaze that destroyed back lot sets, a video library and the "King Kong" exhibit.

The fire, which burned about two city blocks, was not extinguished until about 10pm Sunday.

On Monday morning, 40 to 50 firefighters were still dousing hot spots, County Fire Captain Mike Brown said.

It might take fire officials two or three days to determine whether firefighters' efforts were hampered by the park's sprinkler system or low water pressure, Brown said.

Some firefighters on the scene could get only a 10-foot spray from park hydrants and were unable to reach the flames.

The fire, fuelled by highly combustible facades and lumber, rendered a sprinkler system on outdoor sets nearly useless, Freeman said.

Firefighters resorted to pumping water from two man-made studio ponds, including one that is home to the animatronic "Jaws" attraction. They also snaked hundreds of yards of hoses to street hydrants outside the park.

Universal Studios Hollywood representatives declined to comment about the water-pressure issues.

- Los Angeles Times-Washington Post News Service