A SUV being shown to prospective buyers at a crowded indoor auto auction suddenly accelerated with a screech of its tires and crashed through a wall Wednesday morning, killing three people and injuring nine.

An auction employee in his 70s was behind the wheel of the 2008 Jeep Grand Cherokee when it apparently lurched out of control and mowed people down at LynnWay Auto Auction in Billerica, about 20 miles (32 kilometers) northwest of Boston.

One man and two women were killed in the crash, Middlesex District Attorney Marian Ryan said at a news conference. Nine people were hurt, including two with life-threatening injuries, she said. The driver wasn't hospitalized, she said.

"The preliminary investigation suggests this is a tragic accident," Ryan said.

Massachusetts State Police investigators are working to reconstruct the accident, which happened while several hundred people were in the building.

Woody Tuttle, an auto auction employee who saw the crash, told WCVB-TV that the building has eight lanes in which vehicles on the auction block line up. People were standing between the lanes when one vehicle suddenly took off, Tuttle said.

"I heard a screeching of tires, and, I believe, a Jeep Cherokee went flying by me," he told the station. "In avoiding the cars, whoever was driving this vehicle hit several people."

The vehicle then went through the wall of the building, Tuttle said.

The driver "avoided the cars, and went on to hit the people who were standing between the cars," Tuttle told WCVB-TV.

Car dealer Fredrick Kyazze said he and a colleague had just moved out of the path of the SUV minutes before it tore through the building.

"We heard a bang from where we just came from," Kyazze said. "I thought probably the building collapsed or something like that. Then we ran back to see what was going on and ... we just saw people lying on the floor."

Emergency personnel were quick to respond to the scene because four police officers and a firefighter are routinely stationed at the auction site because of the large crowds it draws every Wednesday, Billerica Police Chief Daniel Rosa said. Ambulances from several surrounding towns responded.

Images from TV helicopters showed a vehicle covered in debris. Medics wheeled people out of the building on gurneys.

In 2015, an SUV driven by an elderly man hurtled through an auto auction in the Boston suburb of Framingham, striking other cars, patrons and a cinder block wall and injuring eight people. No charges were filed.