Rescuers said they did not expect to find any more survivors or bodies Sunday under the twisted wreckage of an exhibition hall in southern Poland that collapsed during a racing pigeon show, killing at least 66 people and injuring 160.

Rescue crews used hand tools for 20 hours in bitterly cold temperatures to carve through the sheet metal and snarled poles of the collapsed building so as not to risk harming any potential survivors.

But Katowice fire chief Kazimierz Krzowski said Sunday that large machinery was being called in to tear down the rest of the building.

"There is a low possibility that people are still trapped under there," Krzowski said after surveying the site. "The parts of the structure that are not lying on the ground are a threat."

Some 1,300 firefighters, police officers and mine rescue workers from around the region were brought in to help in the effort.

The snow-covered roof collapsed Saturday afternoon when about 500 people were in the hall. People trapped in the wreckage used cell phones to call relatives or emergency services and tell them where they were.

One survivor, Tadeusz Dlugosz, climbed out of the rubble only to find out his 26-year-old son, who was visiting another exhibit when the roof collapsed, had been killed.

He was still at the site Sunday morning, trying to find out where his son's body had been taken.

"It was his idea to come to the fair ... and he found his grave there," Dlugosz said. "I don't know which morgue he's in. I would like to see him and take him as quickly as possible."

At least 66 people were killed, said Janusz Skulich, head of the Silesia region fire brigade. The victims included a police officer providing security for the exhibition, police spokesman Janusz Jonczyk said, adding that at least 160 people were injured.

Jonczyk said 51 victims had been identified by Sunday afternoon, including seven foreigners — from the Netherlands, Belgium, Slovakia, the Czech Republic and Germany.

Prime Minister Kazimierz Marcinkiewicz joined several thousand people at Cathedral of Christ the King for a Mass for the victims celebrated by Archbishop Damian Zimon.

People who escaped the disaster said two emergency exits were open but other exits were locked, leaving others trapped.

Witness Franciszek Kowal, who jumped to safety from a terrace 13 feet up, saw people struggling to break windows to escape.

"I saw a macabre scene as people tried to break windows in order to get out," Kowal told The Associated Press. "People were hitting the panes with chairs, but the windows were unbreakable. One of the panes finally broke, and they started to get out by the window."

Attorney Grzegorz Slyszyk, who represents the company that owns the building, said he had no information on the reports, but he vowed to investigate if exits were locked.

President Lech Kaczynski declared a national state of mourning to last through Wednesday.

"This was the greatest tragedy of the third Polish Republic," Kaczynski said.

The "Pigeon 2006" fair had more than 120 exhibitors, including groups from Belgium, the Netherlands, Germany, Ukraine and Poland, according to the fair's Web site. The gathering was devoted to pigeon racing, a sport in which homing pigeons are released and race home using their sharp sense of direction.

The exhibition at the 110,000-square-foot hall in the Bytkow district of the city opened Friday.

Crumpled bird cages were scattered inside the building near the entrance, and dozens of white and brown pigeons perched on the twisted rafters.

Police said snow made the roof collapse, but Slyszyk disputed that. He said snow had been removed regularly and that it was too early to speculate on a cause.

Katowice, some 200 miles south of Warsaw in a mining region, has been hit with the same heavy snow this winter that has been plaguing much of eastern and central Europe.

On Friday, snow caused a town hall's roof to collapse in the southern Austrian town of Mariazell, though no injuries were reported.

On Jan. 2, the snow-covered roof of a skating rink collapsed in the German Alpine spa town of Bad Reichenhall, killing 15 people.