Six people died and up to 10 others were injured after an out-of-control bin lorry careered through streets packed with Christmas shoppers.
Witnesses described bodies lying in the road after the crash in Glasgow city centre, which is being treated by authorities as a major incident.
The lorry travelled from the Gallery of Modern Art before it crashed near the side entrance of the Millennium Hotel next to Queen Street station.
The cause of the crash was not immediately clear but there were unconfirmed reports that the driver, who survived it, might have suffered a heart attack.
Police confirmed the driver was one of those taken to hospital.
Witness Melanie Greg said the lorry travelled 150 yards along the pavement before crashing in George Square.
She said: "The bin lorry just lost control. It went along the pavement, knocking everyone like pinballs. There was a baby in a buggy, and it just continued knocking people down until it ended up in the building. Quite horrific, very scary.
"The only way it stopped was hitting the building.
"People were trying to run out of the way. But when something was coming out behind them like that, how can they run out of the way?"
She added: "There was noise, bangs, screams and everything. It was just horrific."
Superintendent Stewart Carle said the lorry hit several pedestrians.
He said: "It's difficult for all the emergency services but particularly for those people who have been in Glasgow today shopping and getting ready for Christmas.
"There will be a lot of distressed people and certainly the city will need to come round those people that have been traumatised by the incident." Mr Carle said: "About 2.30pm a Glasgow City Council bin lorry was travelling north on Queen Street outside the Gallery of Modern Art when it was in a collision with a pedestrian.
"The bin lorry then has continued north on Queen Street, it would appear to have gone up on the footway and there have been a number of other pedestrians it has collided with."
Scotland's First Minister Nicola Sturgeon said: "My thoughts are with everyone involved in this tragic incident, and especially with the friends and families of the six people who lost their lives in what is another sad day for Glasgow and Scotland."
The tragedy struck barely a year after the Clutha Bar helicopter crash in the city.
Ten people died when a police helicopter crashed on to the roof of the pub on November 29 last year.