Poland is observing three days of national mourning for 66 people who were killed when the roof of an exhibition hall collapsed yesterday.

One hundred and fifty people were injured in the incident, which happened near the southern Polish city of Katowice during an international gathering of pigeon fanciers.

Rescuers have now ended the search for survivors in the wreckage, and an inquiry is underway to establish the cause of the disaster.

Police said the roof may have collapsed under the weight of snow. Another theory is that the extreme cold caused steel beams to fail.

Temperatures in the area dropped to -15C overnight making it more difficult for rescuers to search the rubble. Hot air was blown into the collapsed structure last night in a bid to help any survivors.

More than 1,000 police, firefighters and soldiers were involved in the rescue operation and workers from local mines helped search the rubble of the building which was only built in 2000.

Regional authorities have now brought in heavy machinery to start removing debris.

A fire brigade spokesman said heavy snow on the hall roof appeared to have caused the catastrophe. But a spokesman for the building's management company maintained that snowfall was regularly removed.

Severe weather leaves up to 200 dead in Poland

The region is experiencing its coldest winter in several decades and like other parts of Europe, temperatures have fallen to as low as -30C.

The severe weather has killed almost 200 people in Poland, disrupted transport and highlighted gas supply problems.

This latest accident comes less than four weeks after 15 people were killed in neighbouring Germany when the roof of a skating rink collapsed under the weight of snow.