An illegal drag race in Union City ended tragically early this morning when a vehicle traveling at up to 100 mph hit a woman's car as she made a left turn, killing her and the driver of the speeding car.

The 12:30 a.m. crash at Mission Boulevard near Holly Leaf Lane sent the speeding white Thunderbird and the woman's red Volvo spinning 200 feet, leaving a trail of car parts and debris on the street, said Union City police spokesman Roberto Munoz.

Killed were the driver of the Thunderbird, an unidentified 24-year-old Hayward man, and Zarghona Shokoor, 38, of Union City, whose Volvo was broadsided at a speed of up to 100 mph by the other car, police said.

The crash happened as Shokoor made a left turn in front of the racing vehicles as they traveled north on Mission, not far from the Masonic Home for Adults, a retirement community.

Police were searching for the driver of the other racing vehicle, described only as a blue car.

The tragedy underscored the dangers of illegal drag racing in city streets, in which racers, often young men in souped-up cars, meet at stoplights and dare each other to race.

"Early in the morning, about 6 a.m., people drive fast," said Daniel Rice, 15, as he walked his dog this morning near the crash site. "They're always screeching their tires over there, usually at night."

Union City store owner Nick Dadlani said the crash was the "first I've heard about drag racing here," although he was aware of speeding problems along busy Mission Boulevard, a thoroughfare linking Hayward to Fremont.

Authorities in the South Bay and southern Alameda County have sought to clamp down on street racing, but often the racers move from location to location, bragging on street racing Web sites about the extreme measures taken to prevent police raids.

Some races have ended tragically.

On April 15, Daniel Emery Tobin, 19, was killed while apparently racing his 1986 black Ford Mustang against a 2001 black BMW 330CI driven by Kraig Amador, 21, of Mountain View.

The two were racing on Blossom Hill Road in San Jose when Tobin lost control and slammed into a pole, tearing the car in half and ejecting the teenager onto the road.

That incident came just four days after Sergey Shatsman, 19, was killed in San Francisco when friends in three cars were zooming down 41st Avenue in the Sunset District and a Muni streetcar slammed into a late-model Acura that ran a stop sign.

A movie being released tomorrow called "The Fast and the Furious," stars Paul Walker as an undercover cop hoping to bust street racing.

Chronicle staff writer Benjamin Pimentel contributed to this report. / E-mail Henry K. Lee at hlee@sfchronicle.com.