Police who checked all the locations said no explosives were found and there were no explosions at noon as the e-mails had threatened. One hospital in southern Poland was fully evacuated, one in Warsaw partially.
"The entire day was lost for us and for the patients," said Wlodzimierz Migacz, director of a hospital in Katowice, who ordered a full evacuation, including of a premature baby in an incubator.
"I hope the author of the e-mail will be found and punished," Migacz said on TVN24.
People were allowed to return to the buildings today afternoon.
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Interior Minister Bartlomiej Sienkiewicz said there was no danger to anybody's life or health and that the threats were a case of "unbelievable cheek" on an unprecedented scale.
He said finding the sender was a priority for the police. Some of the e-mails were sent from servers outside Poland, according to national police spokesman Mariusz Sokolowski.
A false bomb threat leading to major disruption carries a maximum prison sentence of eight years.