At least seven people died in the Slovak town of Prešov after a gas explosion on Friday, authorities said.
Fire tore through the top floors of the building and caused the roof and staircase to cave in. The local fire department said rescue efforts were hindered by poor reconstruction.
Rescue workers evacuated 34 people from the building. But one person is still missing.
That person could have been trapped on the top floor, the fire department said.
Prešov Mayor Andrea Turcanova said the town had suffered its biggest tragedy in half a century.
She posted updates about the event to her Facebook page and thanked people for donations of food and clothing.
"It's amazing how many people were ready to help and I really appreciate it," Turcanova wrote on Facebook.
Slovak Prime Minister Peter Pellegrini said in a social media post that €1 million in aid is available for families affected by the fire.
He added that people could contribute to the effort through official links on the town and police website. He warned people to not be fooled by donation scams.