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 bus flipped 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.
Students began helping each other out of the bus through windows and emergency exits. The crash site was just a few blocks from a police and a fire station, and dozens of officers and firefighters were at the scene within minutes.
"They were here almost immediately," Los Angeles Mayor Antonio Villaraigosa said at the news conference. "Thank God for that."
The two people from the BMW were turned over to the California Highway Patrol and were being evaluated for possible injuries, CHP spokesman Miguel Luevano said. He said investigators were trying to determine if drugs or alcohol were involved.
Luevano said there were dozens of witnesses at the intersection, which also is home to a Gold Line light rail stop. Some of them may have helped the construction worker stop the two people from fleeing.
The uninjured 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," said Romero, 16, wearing a white hooded sweat shirt and holding a Hello Kitty book bag. "We actually flew." Romero, who hit her head in two places but was not seriously hurt, said she saw students bleeding, including two of her close friends. She 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.