Survivors of a fire that killed 21 people at a three-story shelter for homeless families in Poland on Monday described a fast-moving inferno that forced some to jump from windows into trees, AP reported. Six of the victims were children and another 20 people were injured, most of whom sustained broken bones after leaping from the building to escape the blaze in the northwestern city of Kamien Pomorski. The cause of the fire, which began around 1 a.m. (2300 GMT Sunday), was under investigation. Police and fire investigators continued to comb through the building's smoldering shell late Monday in search of clues. The first floor was built of concrete and the top two floors had a metal frame. But officials said the walls appeared to be made from a highly flammable material.