The fire broke out just after 2:45 p.m. on some grass located underneath several vehicles at the Hertz rental car overflow lot in South San Francisco.
Residents and lodgers of a nearby motel were briefly evacuated as a precaution. Motel employees went door-to-door to ask customers to leave.
"I thought we were on fire," motel guest April Stewart said. "So I just told my family to get everything and get out. That was before the cops actually started getting people out."
Stewart said she could hear fireworks going off as firefighters approached the scene. Another motel guest, Mike Lavine, said he heard could hear firecrackers.
"About five minutes later, it's all burning away," Lavine said. "That was it."
A fire chief said they are investigating illegal fireworks as the cause of the blaze.
The fire initially consumed eight vehicles, but moderate winds caused the fire to spread to other vehicles nearby. In the end, 37 vehicles were torched as a result of the fire. It's unclear how much financial loss the Hertz will experience as a result of the fire.
The fire was not at the Hertz rental car lot at the airport, but at a satellite parking lot where customers can also pick up vehicles.
There were no injuries.