More than 30 people have been taken to hospital after a police helicopter crashed on to the roof of a crowded pub in Scotland.
Firefighters have been working through the night to rescue people trapped inside the Clutha pub in Glasgow after the roof collapsed on revellers.
Police Scotland said 32 people had been taken to hospitals across the city.
A major incident was declared after the crash at 10.25pm last night and Scotland's First Minister Alex Salmond has warned that the nation must be prepared for the likelihood of fatalities.
The injured have been taken to the Victoria Infirmary, Glasgow Royal Infirmary and the Western Infirmary.
It is not yet known how many are still trapped inside the building.
Deputy chief constable Rose Fitzpatrick said: "Our thoughts are with all those who have been affected by this incident and we are continuing work with our colleagues in the Scottish Fire and Rescue Service and the Scottish Ambulance Service to recover people from the scene.
"A full investigation is now under way however at this early stage it is too early to provide details on why the helicopter came down.
"There were three people on board the helicopter, two police officers and a civilian pilot, and on a busy Friday night, there were a number of customers in the bar.
"We are working hard to recover people still inside the building and we will make further details available when we have them."
Witnesses described how the helicopter dropped out of the sky and on to the roof of the pub in Stockwell Street ''like a stone''.
This is unbelievable. Just spent 20 minutes pulling people out the bar. Apparently a helicopter crashed on the roof. pic.twitter.com/4hoSwgwX2E— Wes (@scotscribbler) November 29, 2013
The aircraft involved was a Eurocopter EC135 T2.
Assistant chief officer Lewis Ramsay, of the Scottish Fire and Rescue Service, said firefighters had made contact with people trapped but it was difficult to tell how many were inside as the building was "very unsafe".
"We've had some contact and we're working away just now to make sure that the building is safe in order to get people out," he said.
"We are determined that we are going to get the building stable and we will be in there to carry out those rescues."
Helicopter crash into Clutha. Praying they'll get everyone out. pic.twitter.com/Me3fQIAsBS— Christina O'Neill (@crushtina) November 29, 2013
A number of casualties had been removed earlier on with a range of injuries, he added.
The "methodical" search and rescue operation involves 125 firefighters including crews trained in shoring up unstable buildings, excavating into collapsed structures and seeking and identifying casualties using specialist equipment.
A full probe involving the Air Accidents Investigation Branch (AAIB) and the emergency services is under way.
Labour's international development spokesman Jim Murphy MP said he saw people "clambering out'' of the bar as he was driving past and jumped out to help.
He said: "There were people with injuries. Bad gashes to the head. Some were unconscious. I don't know how many.
''The helicopter was inside the pub. It's a mess. I could only get a yard or two inside. I helped carry people out.''
Mr Murphy told Sky News that people formed a human chain to help pass unconscious people out of the pub so that ''inch by inch, we could get the people out''.
The bar was busy with revellers enjoying a gig by nine-piece ska band Esperanza at the time of the crash.
Grace MacLean, who was inside the pub, told BBC News: ''They carried on playing and then it started to come down more and someone started screaming and then the whole pub just filled with dust. You couldn't see anything, you couldn't breathe.
''People started coming out with injuries and blood and everyone was going over and trying to help out.
''I don't think it crashed, if it had crashed there would have been fire, there would have been a noise, but we didn't hear anything, it was the smoke that we noticed.
''I think maybe whoever was in the helicopter just tried to land on the roof or something."
The First Minister said the Scottish Government's resilience operation has been mobilised.
"Our thoughts are with everyone involved with the incident in Glasgow," he said.
"However given an incident of this scale we must all prepare ourselves for the likelihood of fatalities."
One image of the crash showed the dark blue helicopter on the roof with yellow police insignia on part of the wreckage.
Helicopter operator Bond Air Services said it was working with Police Scotland.
A large section of the city centre was cordoned off with all roads leading to the junction of Clyde Street, Stockwell Street, Bridgegate and the Victoria Bridge closed.
Police have set up a telephone number for members of the public who are concerned about relatives who may have been involved in the crash. It is 0800 092 0410.