WATCH: School Bus Pushes 5 Cars In Chain-Reaction Crash Outside Of School

An out-of-control school bus caused a six-vehicle chain-reaction crash that left a pedestrian and two others injured outside of Henry Grew Elementary School in Boston, Massachusetts, on Thursday (December 14) morning.

According to WBTS, the accelerator on the bus malfunctioned, causing it to strike a row of parked cars. The driver tried turning off the engine, but it didn't stop the bus.

Surveillance video showed the bus rear-ending the cars in front of it and forcing them forward. An SUV in the middle of the pack turned sideways and went over the curb while its rear wheels rested on the hood of the car behind it.

Officials said all of the students were dropped off at school before the crash.

The injured pedestrian has not been identified. Her sister-in-law, Shanell Saunders, told  WCVB that she was taken to the hospital for treatment.

"She said she ended up under the bus. She got hit, and the bus went over her," Saunders said. "All she heard was the noise, and then, all she said was the next thing, you know, it was black, and that's how she knew she was under the bus."

No information was provided about the other two people who were injured in the crash.

Investigators have not said what caused the accelerator on the bus to malfunction.