SAN MATEO, Calif. (AP) — A limousine traveling on a major bridge in the San Francisco area burst into flames, killing five female passengers who were trapped inside and injuring four others who escaped, authorities said.

The limo was carrying nine women passengers and a male driver when it caught fire late Saturday night on the San Mateo bridge, California Highway Patrol officer Art Montiel told The Associated Press.

Five occupants became trapped, while the four others suffered injuries but managed to get out after the vehicle came to a stop on the bridge, the patrol said. The driver escaped uninjured.

Montiel said that the victims were all in their 30s. Authorities said the names of the dead would be released once families have been notified.

The blaze occurred around 10 p.m. PDT on westbound lanes of the bridge, which connects San Mateo and Alemada counties, about 20 miles southeast of San Francisco.

The patrol said that smoke started coming out of the rear of the limo, and the driver pulled over as the vehicle quickly became engulfed in flames. Officers were trying to determine the cause of the blaze, which wasn't the result of an accident.

"We have no idea right now where they were going or where they were coming from," CHP officer Amelia Jack told KGO-TV.

Two of the four women who escaped were taken to Stanford Hospital and two others were taken to Valley Medical Center in San Jose. All four are being treated for smoke inhalation and burns. The driver was not injured.

The westbound lanes of the bridge were closed as officers investigated the cause of the deadly fire, but the patrol said one lane of traffic reopened early Sunday.