Five women on their way to a bachelorette party were killed Saturday night in an unusual limousine fire in the San Francisco Bay Area.

The women, who authorities will not identify until their relatives are notified of their passing, apparently were unable to get out of the limo, which was set afire in a semmingly bizarre manner, the Los Angeles Times reported. The man who was driving and four other women were able to escape, but they did not include the bride-to-be, the Associated Press said.

“We have no idea right now where they were going or where they were coming from,” California Highway Patrol officer Amelia Jack initially told a Bay Area media outlet, according to KTVU-TV.

The fire is under investigation, as authorities try to figure out what ignited it as the car passed over the San Mateo-Hayward Bridge between Foster City and Hayward. The San Jose Mercury News reported that officials believe the fire began in the rear of the limo, and Bay City News via KGO-TV reported that witnesses said they saw people trapped inside the vehicle shortly thereafter.

CHP officer Art Montiel told ABC News it appears that no car crash preceded the fatal blaze.

"It does not appear that it [the limo] was involved in a collision, so it just appears that it was a vehicle fire," Montiel said.

AP reported the fire took place at about 10 p.m. local time.