San Mateo, California (CNN) -- It could take weeks to figure out why a white stretch limousine caught fire over the weekend, turning a celebratory bachelorette party deadly, authorities said Monday.
Nine passengers were traveling in the Lincoln as it headed across the San Francisco Bay along the San Mateo-Hayward Bridge on Saturday night. Only four came out alive.
The bride-to-be, 31-year-old Neriza Fojas, was among the dead.
"To watch this long limousine just engulf in flames. It was just a nightmare," Ricky Brown, the driver of that vehicle, told CNN's Brooke Baldwin on Monday. He was uninjured.
The limousine showed no sign of problems before it caught fire, Brown said.
Recalling the sequence of events, he said one of the women in the limousine knocked on the partition separating him from the passengers, and said "smoke."
He thought she was asking if she could smoke a cigarette.
"I said, 'Well, we only have four more minutes and, you know, the boss doesn't allow us to smoke in the limo.' About 30 seconds pass, and she knocks again," Brown said.
This time he knew something was wrong.
Smelling smoke, he immediately pulled over.
At least one of the women climbed through the partition. Someone, Brown wasn't sure who, opened the back door. He was able to help one or two of the women out of the burning vehicle.
"Everything happened so fast," he said. "When that back door opened, it just burst into flames."
"I just wish that there could have been something done, more," Brown said.
The vehicle is listed with California's Public Utility Commission as legally carrying eight passengers or fewer, so it was in violation, said Mike Maskarich, commander of the California Highway Patrol in Redwood City.
The driver had the proper license.
"The flames were gigantic," said Roxanne Guzman, who was in a car crossing the bridge about 10 p.m. Saturday. "The flames were so big and radiating so much heat that I could feel the heat off of my face, and I was in my car the entire time."
The four passengers who got out suffered smoke inhalation and burn injuries.
One patient remained in critical condition Monday at Santa Clara Valley Medical Center, while another was in serious condition. The conditions of the other two survivors were not immediately known.
The bodies of the women who died were found in the car, pressed against the partition between the passenger compartment and the driver's area, authorities said.
Fire officials said a crew responded quickly, but it was too late to save them.
"Looking at the photos, it appears it started in the trunk," California Highway Patrol spokesman Ron Simmons said Sunday. "But at this time, we don't know officially if the fire started inside the vehicle or on the exterior."
Lovela Nicolas, the sister-in-law of Fojas' sister, said Fojas was a registered nurse.
"Neriza was getting married, going to the Philippines to get married there and have a ceremony there and the reception," Nicolas told CNN from her home in Honolulu.
Fojas worked with Michelle Estrera at Community Regional Medical Center in Fresno, the center said in a statement. Estrera was also in the limousine and died.
"Neriza Fojas and Michelle Estrera were exemplary nurses who dedicated their lives to helping others. These two outstanding nurses were loved by their patients, colleagues and staff at our hospital," the center said.
The mother of one of the surviving women told CNN affiliate KTVU that her daughter, Mary Guardiano, was upset but physically OK.
"She's very sad. She is crying," said Rosita Guardiano.
In a written statement, the limousine company said it was "deeply saddened" by the deaths.
"LimoStop Inc. will do everything possible to investigate and assist authorities in determining the cause of this fire in order to help bring forth answers and provide closure to the victims and their families," it said.
Medical examiners may need up to two days to positively identify the remains, San Mateo County Deputy Coroner Roger Fielding said.
CNN's Jackie Castillo, Nick Valencia, Jake Carpenter and Justin Lear contributed to this report.