Five other women were able to escape when flames overtook the white limousine last night as it headed west on the San Mateo Bridge, California Highway Patrol spokesman Art Montiel said.
The vehicle was going from Alameda to Foster City when the 10 occupants, all in their 30s, noticed smoke.
The car pulled over; the driver and four others were able to get out, Highway Patrol Officer Amelia Jack told CNN affiliate KGO.
"We have no idea right now where they were going or where they were coming from," Jack said.
More From This Section
Of the survivors, Jack said one had severe burns and three others suffered minor to moderate injuries that included smoke inhalation. The four were rushed to nearby hospitals for treatment, while the fifth person who escaped was not hospitalised.
Some good Samaritans who pulled over and attempted to help were also unsuccessful, the report said.
Several lanes of the bridge were closed as officers probed the cause of the accident. One lane of traffic was reopened early today, police said.