A limousine travelling on a major bridge over San Francisco Bay has burst into flames, killing five women who were trapped inside and injuring four other women who escaped, authorities say. The limo was carrying the nine women and its driver when it caught fire on Sunday on the San Mateo-Hayward Bridge, California Highway Patrol officer Art Montiel told The Associated Press. Five of the women were trapped in the 1999 Lincoln, but the four others managed to get out after the vehicle came to a stop on the bridge, the CHP said. Autopsies were being conducted to determine the exact causes of death of the five who were not able to make it out of the burning limo, said San Mateo County Supervising Deputy Coroner Michelle Rippy. The names of the dead were not expected to be released until Monday. All five were pronounced dead at the scene. The driver of the limo - identified as 46-year-old Orville Brown of San Jose - was the only person to escape unhurt. The CHP could not say early Sunday if Mr Brown was the owner of the limo, or if the vehicle was operated by a limo company. Attempts by The Associated Press to reach Mr Brown for comment were unsuccessful. Investigators have not determined what sparked the fire, but the CHP says the limo became engulfed in flames after smoke started coming out of the rear of the vehicle. It was not clear if any other drivers on the bridge stopped and tried to help those get out, or how the driver managed to escape without injury. ""Four people got out, as far as what was going on inside, I don't know,"" CHP officer Jeremy Lofstrom said Sunday. A photo taken by a witness and broadcast on KTVU-TV showed flames shooting from the back of the white stretch limo. Aerial video shot after the incident showed about one-third of the back half of the limousine had been scorched by the fire, and its taillights and bumper were gone and it appeared to be resting on its rims, but the remainder of the vehicle did not appear to be damaged. The four women who escaped the fire, Jasmine Desguia, 34, Mary Guardiano, 42, Nelia Arrellano, 36, and Amalia Loyola, 48. They were taken to area hospitals where they were being treated for smoke inhalation and burns, the CHP said. Their conditions were not known.The blaze occurred on the westbound lanes of the bridge, which is part of state Highway 92, and runs several kilometres across San Francisco Bay, connecting San Mateo and Alameda counties, about 40 kilometres south of San Francisco.