An SUV being shown to prospective buyers at a crowded indoor car auction in the US suddenly accelerated with a screech of its tyres and crashed through a wall, killing three people and injuring nine.
An auction employee in his seventies 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 32 kilometres (20 miles) north-west 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 was not taken to hospital, she added.
"The preliminary investigation suggests this is a tragic accident," Ms 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 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, Mr Tuttle said.
"I heard a screeching of tyres, 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, Mr Tuttle said.
The driver "avoided the cars, and went on to hit the people who were standing between the cars", Mr 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," Mr 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 stretchers.
In 2015, an SUV driven by an elderly man hurtled through a car auction in the Boston suburb of Framingham, striking other cars, patrons and a wall and injuring eight people. No charges were filed.