The accident was reported at the Metro Silver Line platform right under the 105 Freeway shortly after 3 p.m.
Authorities said a 52-year-old man was driving in the carpool lane when his blue Honda jumped a sidewalk into the bus lane and swerved around a parked bus, slamming into boarding passengers.
Six people were taken to local hospitals with critical injuries. Four of them - three men, ages 30 to 50, and a teenage girl - were brought to Harbor-UCLA Medical Center with potentially life-threatening injuries.
"They range in injuries from head injuries, neurologic injuries, orthopedic injuries and abdominal injuries," said Dr. Wendy Coates of Harbor-UCLA Medical Center.
Brian Tabin's two uncles were injured in the crash. One of the uncles just arrived Wednesday from Canada.
"This is what happens when people rush all the time. Bad things happen," said Tabin.
The driver was transported to a local hospital after being treated at the scene. A field sobriety test was conducted at the scene of the crash.
California Highway Patrol officials don't believe alcohol was a factor in the crash, but they're not certain that the driver wasn't under the influence of drugs.
Charges in the case are pending while the CHP continues its investigation.