(CNN) -- At least one person is dead after a police helicopter crashed into a pub in Glasgow, Scotland, authorities said.
"We expect that number to increase over the coming hours," Chief Constable Stephen House told reporters.
An unknown number of people remained trapped inside the pub Saturday morning, 12 hours after the helicopter crashed as the building was packed with Friday night customers.
At least 32 people were taken to three local hospitals after the incident in Glasgow, House said.
The head of the Scottish government, First Minister Alex Salmond, said it was a "black day for Glasgow and for Scotland."
But, he said, people should take heart from the swift response of emergency responders and the "instinctive courage of ordinary Glaswegians" in the face of adversity.
"As First Minister, it's a day we can take great pride in how we've responded to this extraordinary tragedy," he said. Salmond added that Saturday is St. Andrew's Day, Scotland's national day.
Emergency responders "are working hard to recover people still inside the building," said Deputy Chief Constable Rose Fitzpatrick, of Police Scotland, earlier Saturday.
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The helicopter carrying two police officers and a civilian pilot crashed into the downtown Clutha Bar as it was crowded with revelers, authorities said.
The search for survivors is still ongoing, police said.
House said it will take some time because of the nature of the damage caused.
"This is a very difficult and sensitive operation," he said.
"Everyone was really confused and scared," said Grace Maclean, who was in the pub listening to a band when the crash occurred. "No one had a clue. There was no explosion. No bang. It was really quiet."
The helicopter impacted as patrons listened to the Esperanza band, which had taken the stage a short time earlier.
"Most of the helicopter appeared to be inside the pub," said Jim Murphy, a UK member of parliament who arrived at the site moments later and saw people scrambling out to get out. Murphy represents a portion of Glasgow.
Patrons described a surreal scene followed by confusion.
"We were watching the band and there was kind of like a (roof) panel fell, there was a whoosh of dust, then we laughed that the band said, 'We didn't think we were going to bring the roof down,'" Maclean said. "The roof didn't come down. ...It didn't come completely down anyway."
After the crash, an outburst of noise followed.
"Everyone was yelling (for) their friends, but everyone seemed to find everyone," Maclean said.
Christina O'Neill, who saw the crash from her apartment across the street, said she heard what sounded like a low-flying airplane.
"I thought that didn't sound right for a couple of seconds," she said.
After the sound of impact, she saw smoke and people running from the pub.
"I know there were a lot of people lying on the ground kind of getting looked into," she said.
In a Facebook posting, the band indicated that all its members made it out safe.
"It seems that the band are all OK. Not so sure about everyone else," the post said.
Band manager Gary Anderson described his bewilderment when he heard "a loud bang followed by lots of debris, smoke, stuff coming coming towards where I was standing at the door."
People he knew pulled him outside into the street, he said, where he could see the rotor blades sticking out of the building's roof.
"The fire brigade, paramedics, police were all there within minutes and everybody was just helping folk who could get out, just shouting on them because at this time you couldn't really see much inside, you were just trying to help people out and shouting to them, 'come here, come here' towards the doors," he said.
"There were people staggering out, there were lots of people coming out with blood pouring from their head and covered with all sorts of just debris from whatever it was had happened."
The pub's Facebook page contained numerous posts from people concerned about the incident.
Those trapped in the debris were communicating with rescuers, said Lewis Ramsay of the Scottish Fire and Rescue Service.
Hours after the crash, the helicopter with "police" on its damaged tail was still smoldering.
Bond Air Services, which reportedly owns the helicopter involved, said it was working with police and emergency services.
"Our thoughts are with those who have been affected by this tragic incident," the company said in a statement.
CNN's Greg Botelho, Nic Robertson, Bharati Naik and Elwyn Lopez contributed to this report.
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