Motorcyclist killed after striking car at high speed on I-8.

A motorcyclist was killed Thursday afternoon in a fiery collision on Interstate 8 in Mission Valley, authorities said.

The eastbound motorcycle crashed into a car near Mission Center Road shortly after 4 p.m., according to the California Highway Patrol. Both vehicles then became engulfed in flames.

Passers-by stopped and performed CPR on the downed rider before the arrival of paramedics, who declared the victim dead at the scene. No other injuries were reported.

Witnesses told officers the motorcyclist was weaving across the road, possibly trying to merge onto nearby Interstate 805, at speeds up to about 100 mph just prior to the collision.

The crash left the entire eastbound side of the freeway blocked in the area for a time, snarling rush-hour traffic.