A roof on an exhibition hall has collapsed killing at least 60 people. A number of foreigners and children are said to be among the dead. Rescue workers are still struggling to free dozens more pinned under the rubble in freezing conditions. Hot air is being blown into the collapsed structure to increase the chances of survival for those trapped. Around 140 people are being treated for injuries.The accident happended when the metal roof of the modern building came down during a gathering of hundreds of pigeon enthusiasts from across Europe. The exhibition hall is located in Chorzow, a town near the southern city of Katowice. Poland is experiencing its coldest winter in several decades and like other parts of Europe, temperatures have fallen to as low as minus 30 Celsius. Authorities say the weight of snow on the roof caused the collapse, but the building’s manager told Polish television that snow had been regularly cleared from the roof.