The death toll rose to 51 from the collapse of a supermarket roof in the Latvian capital Riga, as the search continued for survivors in the rubble, dpa reported.
It was not clear how many people were still missing after the accident. The mayor estimated that about two dozen people could still be buried. President Andris Berzins spoke of an "unimaginable tragedy."
Local media called the collapse of a large section of the building's roof the worst accident since Latvian independence in 1991.
Latvian police chief Ints Kuzis gave three possible reasons for the collapse: the structure of the building had been poorly analysed, ongoing construction, and poor planning.
The government excluded the possibility that natural catastrophe or an act of terrorism had caused the accident.
Rescue work was to continuing into Saturday. Searchers still had another 400 square metres to comb through of the shopping center's 1,500-square-metre collapsed area.
Around 100 people remained at the site despite the damp cold and fog of the night, largely relatives hoping for signs of life. Intense spotlights lit up the rubble.
Across Riga, church bells rang in memory of the dead. In the city centre, people laid flowers and letters at the foot of the freedom memorial.
"We are with you during this tragedy," someone had written on one note.
More than a dozen lawyers launched a volunteer initiative to support family members of the victims with free legal advice, the bar association said.
The Maxima supermarket in central Riga was full of shoppers when the roof caved in Thursday evening.
Witnesses said they heard an alarm before the collapse. Gintaras Jasinskas, a board member of supermarket operator Maxima Latvia, said nobody had been evacuated because there were "no obvious signs of fire," BNS reported.
The operator indicated that about 10 alarms had sounded through the afternoon, according to a spokesman.
Police were investigating the operator for failure to react to warnings.
Thirty-five people rescued from the rubble since yesterday were hospitalized as officials sought more blood donations.
Among the dead were three firemen and at least seven volunteers who were killed when additional sections of the roof collapsed as they worked. An employee of the local rescue service spoke of a complicated and dangerous situation.
The building looked like a house of cards, with the flat roof caving in a minimum of 500 square metres, explained vice mayor Andris Ameriks.
Soldiers searched the rubble and workers moved debris using special cranes. Many residents laid flowers in front of the fence surrounding the area and lit candles.
Latvian media reported that the roof had been undergoing reconstruction. The building was only completed in 2011.
Authorities obtained video footage from security cameras, the police chief said. The data is being analysed by experts to understand the cause of the collapse and to help locate any remaining survivors.
Prime Minister Valdis Dombrovskis ordered three days of state mourning. On Monday, a moment of silence for the victims is to be held across the Baltic country.
Neighbouring Lithuania and Estonia plan to lower their national flags to half mast on Sunday in commemoration. Latvian embassies around the world opened condolence books for messages and signatures.