Two brothers were killed and a third was battling for his life early Monday after a car careened off Highway 92 and slammed into a guardrail, authorities said.

Officer Art Montiel said the driver of the vehicle was also killed. His relationship to the brothers was not immediately known.

Officers responded to a report of a crash on eastbound Highway 92, just west of the Foster City Boulevard exit, at about 9:45 p.m. Sunday, Montiel said.

A 21-year-old San Mateo man driving was traveling on eastbound Highway 92 when he lost control of the car. The car hit the guardrail and overturned, then crashed into a utility pole, Montiel said.

Five people were in the car, including three brothers, of Redwood City, sitting in the back seat. Two of the brothers, ages 12 and 16, were pronounced dead at the scene. The other brother, 18, was transported to a hospital with major injuries.

The driver was also transported to a hospital where he was pronounced dead, Montiel said.

None of the victims' names have been released.

One passenger, an 18-year-old San Mateo man sitting in the front passenger seat, suffered minor injuries, Montiel said. He was wearing his seatbelt at the time of the crash.

It is unknown whether any of the other passengers were wearing their seatbelts, he said.

Investigators have not ruled out that alcohol or drug impairment led to the crash, Montiel said.

Anyone who may have witnessed the crash is asked to call the CHP Redwood City area office at (650) 369-6261.