Latvian President Andris Berzins described Thursday's roof collapse at a supermarket in the capital of Riga as "basically mass murder."

"This incident is basically the mass murder of a large number of defenseless civilians. We must act accordingly,'' Berzins said.

The collapse, which happened during peak shopping hours, killed at least 53 people.

The disaster is already the worst Latvia has seen in decades.

Part of the roof caved in at around 6 p.m. local time on Thursday, according to the BBC, when the 5,000-square-foot store was busy with customers. Some 20 minutes later, another part of the structure collapsed.

Three of the dead were emergency workers who were trying to free people from the rubble at the time of the second collapse, officials said.

Rescue efforts continued through Thursday night, with an unknown number of people feared trapped.

By midday Friday, Latvia's emergency services said 38 bodies had been found. At least 38 people were wounded, according to Reuters.

Rescuers are proceeding cautiously for fear of another collapse, a spokeswoman said, comparing the parts of the supermarket still standing to "a house of cards [that] could easily collapse further if a wrong piece is moved or lifted."

"Every hour, air temperature, high air moisture — they are factors that reduce possibility to find some survivor. But, of course, hope always remains," Armands Plorins, chief of emergency ambulance service told TV.

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Witness Anita Daukste told the BBC: "It was crashing, most people started crying and screaming. It was certain that those left inside after the first collapse would not be alive after the second fall."

A winter garden was being constructed on the roof and some reports suggested the weight of the soil on the roof may have contributed to the collapse, according to the Baltic Times, although nothing is yet confirmed.

Police have opened a criminal investigation, the BBC said.

"It is clear that there has been a problem with fulfillment of construction requirements," Latvia's interior minister, Rihards Kozlovskis, told national TV.

Three days of national mourning were declared from Saturday.