A fast-moving fire tore through a three-story building housing homeless families in northwestern Poland early Monday, killing at least 21 people and injuring 20 more, including an infant, officials said. "I couldn't breathe, so I opened the window and looked out, and the door was on fire because it was essentially made of paper," a survivor told reporters at the scene in footage shown on TVN24 television. "I put my pants on and boots, and a friend gave me a jacket, and there wasn't any more time because it was burning like a torch. Some people jumped into the trees," the unidentified middle-aged man said. The blaze broke out around 1 a.m. in a shelter for people waiting for social housing in Kamien Pomorski, 370 miles (600 kilometers) northwest of the Polish capital and near the Baltic Sea coast, said Pawel Fratczak, a spokesman for Poland's national firefighters. "While searching the building again this morning, we found the bodies of three more people, raising the toll to 21 dead," Fratczak said. "It is going to be hard to identify many of them quickly because they are so badly burned." Footage broadcast on TVN24 taken when firefighters first arrived on the scene showed the stone and metal building engulfed in flames, while in later video firefighters picked through the building's charred, gutted shell with axes. It was not immediately clear what caused the blaze, but police and fire investigators were examining the scene for clues. There were 77 people registered as residents in the building at the time of the blaze. Fratczak said not all were yet accounted for, and that the death toll could rise. The injured, many of whom suffered broken bones after jumping out of windows on the upper floors to escape the blaze, were taken to local hospitals. Two people were being treated for burns, including an 8-month-old baby. The injuries are not considered life-threatening, Fratczak said. "I'm in shock. The most important thing is that we're alive and that the kids are alive," a woman lying in a hospital bed with burns visible on her face told TVN24 through tears. "I'm just worried what happens now. We lost everything. We have nothing. I hope there is somebody who will help not only us, but everyone who has suffered from this because this is truly a tragedy." Prime Minister Donald Tusk flew to Kamien Pomorski early Monday to inspect the damage, and promised aid for those who escaped the blaze. Many of the residents had been living at the temporary housing shelter for a long time as they waited for a permanent apartment in Poland's crowded social housing network. "The help will be full and will ensure the housing needs of those who survived this disaster," Tusk told reporters in front of the still smoking building. "The most important thing is to help those who survived, but ... we still cannot say with full certainty say that the list of those killed is final." President Lech Kaczynski declared three days of national mourning to start at midnight, and was also on his way to Kamien Pomorski.