Six people have died after an out-of-control bin lorry careered through streets packed with Christmas shoppers, knocking down pedestrians "like pinballs".

Witnesses described bodies lying in the road after the tragedy in Glasgow city centre which is being treated by authorities as a major incident.

Police Scotland said six people had been killed and eight people had been seriously injured.

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 of the bin lorry was one of those taken to hospital.

By Monday night, police had erected a steel cordon around the scene of the crash.

First Minister Nicola Sturgeon said flags on Scottish Government buildings would fly at half mast, and plans were under way for a special church memorial service. Reverend Alastair Duncan will lead the service at St George's Tron at 11.30am.

The Christmas lights in George Square were also switched off as a mark of respect.

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.

A Police Scotland statement said: "Regarding a major road incident in George Square, Glasgow, please note that we can confirm that six people have been fatally injured as a result."

Witness Melanie Greg said the lorry travelled 150 yards along the pavement before crashing in George Square.

She told Sky News: "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 as it careered along the road.

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 that at "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."

John Maclennan said: "Seeing injuries in Royal Exchange Square, bin lorry ran all the way up Queen Street into George Square, awful."

Police Scotland have set up a number for anyone who has concerns that their family and friends might be involved in the incident: 01786 289070.