Helicopter wreckage with Police insignia
A helicopter, thought to be a police aircraft, has crashed into a pub on the banks of the River Clyde in Glasgow.
The crash happened at the Clutha Vaults in Stockwell Street.
Jim Murphy, shadow development secretary, said there had been multiple injuries and reported a "pile of people" clambering out of a pub.
Images of the crash on social media sites showed the dark blue helicopter on the roof with yellow "POLICE" insignia on part of the wreckage.
The Police Roll of Honour Trust tweeted "Our thoughts are with the crew of @policescotland SP99 helicopter that has crashed in Glasgow - hoping everyone is alright."
Eyewitness Fraser Gibson, 34, was inside the Clutha pub with his brother to see his former band, Esperanza.
"Midway through their set it sounded like a giant explosion," he told BBC Scotland.
"Part of the room was covered in dust. We didn't know what had happened. We froze for a second; there was panic and then people trying to get out the door."
Mr Gibson said that immediately following the incident there was a suggestion that a helicopter had crashed into the roof of the pub.
"There was no obvious sign of that," he said. "I couldn't hear of any rotors or anything like that before the event happened or any sign when we came out of the pub."
I can't really believe what's happened. I was on the
phone at the time and I heard a misfiring engine.
Looked above me, couldn't work out where it was
coming from, it got louder and louder and I just spotted
a helicopter falling from the sky.
It was falling at great speed. It looked like the rotors
weren't spinning but the helicopter was sort of turning in
a strange position and dropping at great speed. Oddly
enough here was no explosion no fire ball.
It's a busy Friday night, a lot of people have been out in
the pubs, there are a lot of pubs in that area. I do fear,
I would be staggered if there weren't fatalities from the
area it's landed.
"I would say there was maybe 120 people inside the pub. A lot of people managed to get out straight away, but it was hard to tell how many were actually trapped in the other half of the bar.
"We wanted to get out of the way and let the emergency services get in there to help.
"I spoke to one of my former band members and he's as much in the dark over the situation as me.
"We checked that each other was safe and the rest of the band were safe. The immediate group I was with are all safe.
"We're obviously very concerned about what casualties have been sustained in the incident.
"There were no signs (of a helicopter) at all. The roof had just totally collapsed, there were shards of wood sticking out the top but nothing that said there had been a helicopter crash."
A Scottish Fire and Rescue Service said: "I can confirm that we have people at the scene.
"It is obviously a major incident. There are numerous fire engines there; 15 fire engines at the moment along with specialist services.
"I cannot confirm if there have been any injuries."
Claire Morris, who lives near the Clutha bar, told BBC News: "We heard this bang. We didn't really know what had happened and then we heard people coming out and screaming.
"I wasn't sure whether there had been an explosion. My daughter said to me it was a helicopter that had hit the roof.
"Police are everywhere. We are just very shaken."
She added the pub was very popular and would have been busy on a Friday night.
Mr Murphy said there were about 40 fire brigade staff at the scene and said passers-by had helped at the scene.
Mr Murphy told the BBC: "It's a well established Glasgow pub. It's a horrible, horrible scene, but well done to the folk who were here. Everyone formed a chain of people from inside the pub to outside, and the fire brigade and everyone were here very quickly."
First Minister Alex Salmond tweeted: "The emergency services are in full operation. Our thoughts are with everyone involved. Scottish resilience operation now mobilised."
Deputy First Minister Nicola Sturgeon said it was "absolutely awful news".
The crash happened at a pub in the centre of Glasgow
"My thoughts are with everyone involved and the emergency services," she tweeted.
Prime Minister David Cameron tweeted: "My thoughts are with everyone affected by the helicopter crash in Glasgow - and the emergency services working tonight."
Ed Miliband said it was "shocking news from Glasgow. All my thoughts are with those who have been injured."