LONDON — A police helicopter crashed into the roof of a crowded Glasgow pub, causing “numerous” casualties and leaving people trapped in the unstable building, officials said early Saturday.Authorities said they had made contact with people still inside The Clutha pub in the city center. They said some people had been taken to hospitals but that it was too soon to give a number of injured. Witnesses spoke of people streaming out of the building covered in blood, with gashes and other injuries.“Given an incident of this scale we must all prepare ourselves for the likelihood of fatalities,” Scotland’s leader, Alex Salmond, said on his official Twitter account.Television images showed what appeared to be the helicopter’s propeller sticking out of the popular one-story pub’s roof.The crash Friday at around 10:30 p.m. local time sent dozens of patrons fleeing through a cloud of dust.It was unclear how many people were still inside, Asst. Chief Officer Lewis Ramsay with the Scottish Fire and Rescue Service said. He said teams — including 125 firefighters on the scene — were working to stabilize the building and “get people out.”A crew of three — two police officers and a civilian pilot — were aboard the Eurocopter EC135 T2, according to Scottish police. Deputy Chief Constable Rose Fitzpatrick said it was too early to offer details on why the helicopter came down.