Eight people are believed dead and many more injured after a helicopter crashed through the roof of a packed pub on the banks of the River Clyde in Glasgow on Friday night, leaving customers trapped inside.

The helicopter was a police aircraft, with at least two police personnel and a civilian pilot on board

At least 120 people are believed to have been in the busy Clutha pub, which was hosting a live music event, when the crash took place at about 10.30pm GMT on Friday.

Scotland's first minister Alex Salmond said: "I can confirm that it is a police helicopter which has been involved in the tragic accident in Glasgow. Rescue efforts are in full operation. Given an incident of this scale we must all prepare ourselves for the likelihood of fatalities."

The cause of the crash is unclear. A vast area in the city centre has been cordoned off.

A Police Scotland spokesperson said: "A major incident has been declared after the Eurocopter EC135 T2 - with a crew of three consisting of two police officers and a civilian pilot - came down on the roof of a pub in Stockwell Street at 10:25pm."

"Emergency services responded immediately and remain at the scene at the present time. Cordons have been put in place to allow the rescue operation to take place."

The Scottish Fire and Rescue Service is treating a number of people for multiple injuries. At least 32 people are thought to have sustained serious injury, and an unknown number of people may still be trapped inside.

Eyewitnesses described scenes of horror as the helicopter came down.

"There was no bang, no explosion and then there was what seemed like smoke and we were all joking that the band had made the roof come down and then it started to come down more and someone started screaming and the whole pub filled with dust and you couldn't see anything, you couldn't breathe," Grace Maclean, who was in the pub during the crash, told the BBC.

Gordon Smart, the editor of the Sun's Scottish edition, was nearby. He told Sky News: "I was in a car park and looked up and saw a helicopter which I think was a police helicopter.

"There was no fireball and I did not hear an explosion. It fell like a stone. The engine seemed to be spluttering."

Police Scotland have also opened an emergency Casualty Bureau number - 0800 092 0410 - for the relatives of people who may have been present in the pub or in the area.