Updated

LOS ANGELES -- A pedestrian was killed and at least 19 people were injured Monday when a black BMW ran a red light and broadsided a school bus, causing it to flip on its side, east of downtown Los Angeles, police said.

The pedestrian was crossing the street at an intersection in the Boyle Heights area when struck. The person died at the scene, Police Chief Charlie Beck said at a late afternoon news conference.

The bus driver was initially taken to a hospital in critical condition but later was upgraded to serious condition, authorities said. Eighteen high school students on the bus also were taken to hospitals with non-life-threatening injuries.

Twenty-five other students on the bus were not hurt.

The crash occurred at about 3:20 p.m. as the Roosevelt High School students were heading back to school from the East Los Angeles Skills Center, where they attend classes because of overcrowding.

Two people in the BMW fled on foot after the crash and were detained by a local construction worker, who held them until officers arrived, Beck said. They were turned over to the California Highway Patrol and were being evaluated for possible injuries, Beck said.

The noninjured students were taken to the nearby Hollenbeck police station, where they were interviewed by police and firefighters before being reunited with family members.

Television reports showed passengers being loaded onto gurneys at the crash site near the bus, which was lying on its side straddling the sidewalk and a portion of the road.

Susana Romero, an 11th-grader at Roosevelt, was on the bus when the crash occurred. She said she had no warning before hearing a loud crash and feeling the bus tip over.

"We were in the air. We actually flew," said Romero, 16, as she held a Hello Kitty book bag.

Romero said she saw students bleeding, including two of her close friends, and heard more sobs than screams.

"There was crying, but we were very protective of each other and helping each other out as we got off the bus," Romero said. She said she and other students helped some of the injured kids out through the back emergency exit.

Eleven fire companies, eight ambulances, two fire battalion command units, one air ambulance and one heavy rescue unit responded to the crash site.