UNIVERSAL CITY, CALIF. -- Universal Studios opened its gates to tourists Saturday as investigators sought the cause of a suspicious fire that destroyed a block of old movie sets valued at $2.5 million.

Arson investigators were on the scene, said Los Angeles County sheriff's Deputy Pete Fosselman. Detectives also were investigating a bomb threat made shortly before the fire erupted Friday night.

No injuries were reported, but about 200 people watching a taping of a new television series were evacuated along with 75 studio employes.

Arson "is a possibility," said Assistant Fire Chief Ray Shackleford.

Officials said firefighters also were looking for explosives that were supposed to be in a storage area on the site, but the result of that search was not immediately available.

The fire erupted on the set of the 1960 movie "Spartacus" and ran through European Street, a full block of European-style fac ades that included backdrops for the 1931 classics "Dracula" and "Frankenstein."

Although the Universal Studios tour continued as usual, reporters and photographers were not allowed on studio property Saturday. The tour is a tram ride through parts of the studio lot.

A half hour before the fire, Universal's Stage 44 received a telephoned bomb threat, said Deputy Dan Cox.

"When sheriff's deputies arrived to investigate, the fire had broken out," said Cox.

The fire started in the northeast section of the 420-acre studio complex, 11 miles northwest of downtown Los Angeles. None of the sound stages was burned.

County fire dispatcher Eduardo Hernandez said he had heard unconfirmed reports that labor problems may have played a role in the fire.

Dan Slusser, senior vice president and general manager of Universal Studios, declined to comment on any possible labor problems, saying only that an investigation would reveal the cause.

"The damage will probably not affect our shooting schedule," Slusser said. "It's a business of illusion and we'll find a way around it."

European Street, constructed in 1930 and rebuilt in 1968 following a fire the year before, is one of the more popular sets, said studio Manager Bill DeCinces.

The sets were used only a few weeks ago for the recently completed film "Cross My Heart," starring Martin Short and Annette O'Toole, Roach added.

Roach said it would take months to rebuild the destroyed sets.

About 200 people watching a taping of a new television show, "Out of This World," were evacuated, fire officials said.

Officials estimated damage to lighting and other equipment inside the structures at $500,000, and damage to the sets themselves at $2 million.

About 125 firefighters from 30 engine companies contained the blaze within a half hour.