Emergency teams are now sifting through the wreckage of the building
At least 21 people have been killed in a fire at a hostel for homeless people in north-western Poland, officials say.
Another 20 were injured in the blaze in the town of Kamien Pomorski, 60km (37 miles) east of the border with Germany, which began in the middle of the night.
Many of the injuries were sustained as residents jumped from upper floors of the three-storey building.
At least 77 people were registered at the hostel, waiting for the local authority to provide them with housing.
Emergency teams are now sifting through the wreckage of the building. The cause of the blaze is not yet known.
Firefighters had to catch children thrown through windows by their parents
Daniel Kopalinski, rescuer
Prime Minister Donald Tusk broke off his Easter holiday to fly to Kamien Pomorski to inspect the damage and visit the survivors in hospital, whom he said would receive new housing and aid.
He also promised to personally oversee the investigation into the fire, one of the deadliest in living memory. The hostel was built in the early 1970s as a workers' hotel and Mr Tusk questioned whether anyone should have been living in such an unsafe building.
"From what we can tell at the moment, the fire brigades reacted as fast as possible and in a very professional manner. There are situations when chances for a successful rescue operation are little, especially in such a flammable building," he told reporters.
"But a commission will decide if people should have been living in this building and I will be personally overseeing this matter because I know that in Poland there are a lot of places like this, too many."
President Lech Kaczynski also visited the town and declared three days of national mourning to start at midnight.
The fire broke out in the three-storey hostel at around 0100 (2300 GMT on Sunday) and spread rapidly. Witnesses said the building went up like a torch.
Emergency teams said the cause of the overnight blaze was not yet known
"The fire spread at an incredible speed," Daniel Kopalinski, a member of the local emergency services told TVN24.
"Firefighters had to catch children thrown through windows by their parents," he added.
One of the survivors said those inside were forced to jump because the rescuers' ladders had only reached the first floor.
"I yelled to my sister on the second floor 'Jump, I will catch you', but she didn't. Then it was too late," Dariusz Janyszko told TVP.
It eventually took 21 fire crews to extinguish the flames several hours later. The top two floors of the hostel were completely destroyed.
One of the injured is in a serious condition. Many, including one child, are suffering from burns and the effects of smoke inhalation.
Officials said not all of those registered as residents of the hostel had yet been accounted for, and that the death toll might still rise.
A fire service spokesman said it would be difficult to identify many of the victims quickly because their bodies had been so badly burned.
Some of those killed had been visiting family for the Easter holidays.
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