Polish President Lech Kaczynski has called the roof collapse at an exhibition hall the worst tragedy to strike post-communist Poland.
Sixty-six people were killed and at least 141 others injured when the roof of an exhibition hall in the city of Katowice caved in Saturday evening.
The hall was hosting a pigeon racing exhibition and a number of foreigners are among the victims.
President Kaczynski declared three days of mourning and has canceled Monday's scheduled visit to the Czech Republic.
Pope Benedict and Russian President Vladimir Putin have sent messages of condolences.
Polish authorities say they do not expect to find any more survivors in the wreckage.
They say heavy snow piled on the roof may have contributed to the collapse.
Some information for this report was provided by AFP, AP and Reuters.