SAN MARCOS, Calif. - A young man was killed Thursday when the car he was driving careened off a San Marcos street and crashed into several trees, a sheriff's sergeant said.

The crash in the 1000 block of East Mission Road occurred shortly after 2:30 p.m. The driver, believed to be in his late teens or early 20s, died at the scene. His name was not immediately available.

According to witnesses, the youth may have been racing another motorist just before the crash, sheriff's Sgt. Mark Foster said. The other involved driver -- if there was one -- did not stop, the sergeant said.

Deputies shut down a roughly half-mile stretch of the street to allow for the investigation and cleanup.