The victims died desperately trying to scramble through a partition to the driver's section of the limo, which was en route to a wedding party near San Francisco on Saturday night, a coroner said.
Four passengers survived. The driver of the limo was quoted as saying he initially thought the women, reportedly all nurses, were asking him if they could smoke, but misheard them because they were playing loud music.
The victims' bodies were found up against the partition at the front of the vehicle, which caught fire on the Hayward-San Mateo Bridge, across San Francisco Bay.
"This particular vehicle is listed .. as for carrying eight or fewer passengers .. there were nine people in this vehicle," California Highway Patrol (CHP) captain Mike Maskarich told reporters.
According to media reports, 31-year-old newly-wed Neriza Fojas was traveling with eight friends in their 30s and 40s to a wedding shower in nearby Foster City when the limo burst into flames.
The cause of the blame is still not clear. The San Francisco Chronicle quoted the driver, Orville Brown, as saying he initially misheard when one of them tried to get his attention through the partition.
"They had the music up in the back, and I figured she was asking, 'Can I smoke?'" he told the newspaper. "I said, 'The owner doesn't allow smoking in the car, and we only have four minutes to the destination.' "
Less than 15 seconds later the women knocked again, he said. This time, when he rolled down the partition, they were shouting, "Smoke, smoke!" and "Pull over, pull over!"
He helped some of the survivors to safety but was unable to save the women in the back. "We got out by the grace of God. I just wish that I could have done more," the newspaper cited him as saying.
Speaking to CNN, the driver added: "To watch this long limousine just engulf in flames. It was just a nightmare."
San Mateo County Coroner Robert Foucrault said the bodies of the victims "were found forward of the limousine in between the partition, the passenger compartment and the driver's compartment.
"When we got there ... they were up against the partition .. They were getting away from the fire and that's why they were in the front, towards the partition.
"You could also probably say that they were trying to get out," added Foucrault, who told the Chronicle: "This is one of the most horrific things I've seen in 21 years with this office."
Maskarich said it was too early to say whether criminal charges would be brought over the tragedy. "It's going to depend on what we find in the course of the investigation," he said.
Fojas, who lived in Fresno, California, had recently married and had planned to return to her native Philippines for another ceremony next month, according to the Chronicle.
The hospital where Fojas worked, the Community Regional Medical Center in Fresno, said she and her colleague Michelle Estrera, who also died, "were exemplary nurses who dedicated their lives to helping others."
"This horrible accident was a tragic event for so many people and our thoughts and prayers go out to all the nurses involved in the fire and their family and friends," it said in a statement.