BILLERICA, MASS. (WHDH) - An SUV unexpectedly accelerated down a lane inside the Lynnway Auto Auction building in Billerica Wednesday morning and struck several people before slamming through a concrete wall.

Authorities say emergency crews responded around 10 a.m. to 400 Charter Way for a report of a “mass casualty situation.” About 1,500 people were said to be attending the auction.

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Three people, including a man and 2 women, were killed when an employee in a 2006 Jeep Cherokee suddenly lurched forward at a very high rate of speed, hitting a crowd of people, Middlesex District Attorney Marian Ryan said. She said 9 other people suffered injuries, two of whom suffered life-threatening injuries.

Massachusetts State Police say evidence suggests that the incident was not an intentional act. They say the employee, in his 70s, mistook the accelerator pedal for the brake pedal as auto dealers viewed the SUV.

A witness tells 7News that he heard tires screeching before the car drove into a crowd and crashed clear through a wall, saying it sound like an “explosion.” Ryan said the Jeep traveled the length of the warehouse before it crashed. The driver was not hospitalized.

Multiple ambulances and medical helicopters were called to the scene. Medics could be seen wheeling people out on gurneys. Four people were taken to Lahey Hospital in Burlington, where one of the victims died from injuries suffered in the crash.

Ryan said police officers and fire officials were working detail when the crash happened, and jumped in to help immediately.

A crash reconstruction team, as well as state police detectives from the district attorney’s office, are investigating. The Occupational Safety and Health Administration (OSHA) arrived on the scene Wednesday as well.

Ryan and police officers at the scene called the incident “very tragic.”

The Jeep involved in the crash was towed away from the scene on Wednesday evening.

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