Glasgow, Scotland (CNN) — A police helicopter crashed into the roof of a pub crowded with Friday-night revelers in the Scottish city of Glasgow, causing a chaotic scene as patrons ran out and first-responders rushed in.
There were no immediate official reports of casualties, but witnesses reported seeing people who appeared injured running from The Clutha pub after the crash.
"I know there were a lot of people lying on the ground kind of getting looked into," said Christina O'Neill, who lives across the street from the pub.
Pictures posted to social media showed a number of fire trucks, police cars and ambulances surrounding the one-story building, with the remnants of the helicopter wreckage visible from above.
The crash occurred after 10 p.m. local time as patrons listened to the self-styled ska band Esperanza, which had taken the stage at the pub a short time earlier.
"Basically I heard what sounded like a plane going too low, and I thought that didn't sound right for a couple of seconds," O'Neill said.
"Then I just heard a massive crash...I looked out to the car park and thought it might have been just a car crash. It does sound quite devastating at the moment."
O'Neill said after the sound of impact, she saw smoke and people running.
Hours after the crash, the helicopter -- bearing the word "police" on its damaged tail -- was still smoldering.
"I can confirm that it is a police helicopter which has been involved in the tragic accident in Glasgow," the head of the Scottish government, Alex Salmond, said in a post on his official Twitter account.
In another post, he said: "Rescue efforts in full operation. Given an incident of this scale we must all prepare ourselves for the likelihood of fatalities."
A spokesman for the Scottish Ambulance Service told CNN that there were "multiple ambulances and a special operations team on site."
The Clutha's Facebook page contained numerous posts from people concerned about the incident.
"Stay with it everybody, now is the time to think of others," wrote one person. "People need help."
British Prime Minister David Cameron also tweeted about the situation.
"My thoughts are with everyone affected by the helicopter crash in Glasgow -- and the emergency services working tonight," he said.