The driver — 46-year-old Orville Brown of San Jose — was the only person to escape unhurt.
Brown's brother told the Chronicle the flames spread before he could help the women escape.
"He told me, 'Man, it was so fast.' He said, 'I've never seen anything like it in my life.'"
"He kept saying, 'I should have done more, I should have done more," he added.
The brother said that Brown is an experienced commercial driver who has operated big rigs and moving trucks and has a clean record.
The bodies were so badly burned that medical examiners will have to identify the victims by using dental records. Foucrault said the autopsies will include toxicology tests, as well as examinations into whether any accelerant such as alcohol or gasoline was found on the bodies.
The four other women who escaped the fire, Mary G. Guardiano, 42, of Alameda; Jasmine Desguia, 34, of San Jose; Nelia Arrellano, 36, of Oakland; and Amalia Loyola, 48, of San Leandro, were being treated at nearby hospitals, the CHP said.
Desguia and Loyola were listed in critical condition, said Joy Alexiou, a spokeswoman for Valley Medical Center. The condition of Arrellano, who was taken to another hospital, was not known.
A spokeswoman for Community Medical Center in Fresno said one or more of its employees were in the limo.
The company that operated the limo was identified as Limo Stop, which offers service through limousines, vans and SUVS.
The company issued a statement saying it "will do everything possible to investigate and assist authorities in determining the cause of this fire in order to bring forth answers and provide closure to (the) victims and their families."
According to records from the California Public Utilities Commission, which regulates limousine companies, Limo Stop is licensed and insured.
AP reporter Daisy Nguyen contributed to this report from Los Angeles.