(ABC News) -- Authorities are investigating today what caused a stretch limousine to burst into flames, killing five women as it crossed a San Francisco-area bridge.
Nine female passengers were in the limo, along with a male driver, when it caught fire in the westbound lane of the San Mateo bridge late Saturday, California Highway Patrol officer Art Montiel told ABC News.
The fire is believed to have started in the back of the car and quickly spread, but the cause of the fire was under investigation, Montiel said.
"It does not appear that it [the limo] was involved in a collision, so it just appears that it was a vehicle fire," he said.
Four women escaped the limousine and were being treated at two area hospitals for smoke inhalation and burns, Montiel said. He said the driver was not injured in the blaze.
The names of the victims have not been released and authorities said they are uncertain of the womens' plans for the evening.
"We have no idea right now where they were going or where they were coming from," California Highway Patrol Officer Amelia Jack told ABC News station KGO-TV in San Francisco.
The name of the limousine company was not released, but the vehicle was described as a white Lincoln and was said to have been booked from a San Jose, Calif., company.