Latvia store collapse: Deaths rise as Riga rescue continues
Rescue efforts are continuing and police have launched a criminal investigation into Thursday's collapse.
Three of those killed were emergency workers who were helping people trapped when more of the roof came down.
It is the deadliest disaster in the former Soviet republic since it became independent in 1991. Police expect the death toll to rise further.
It is unclear how many more people could still be inside, and the rescue effort is likely to go on through the night.
Latvia's government has declared there will be three days of mourning starting on Saturday.
The cause of the collapse is unclear, although building work was being carried out and a garden was being constructed on the roof at the time.
British pilot Paul Tribble, 27, was shopping in the store when the roof fell in.
"I was taken down by shelving falling on me, which skimmed my shoulder and forced me to the ground but I was still able to move," he told the BBC.
"There were torrents of water coming down off the roof. We headed into the back of the supermarket, the aisles were covered in produce and concrete and people lying on the floor."
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Mr Tribble said a crane had been loading sand and building materials onto the roof in recent weeks. He said he believed a lack of drainage following heavy rains had contributed to the fall.
Prime Minister Valdis Dombrovskis, who visited the scene on Friday, said: "The criminal process has started about violating building standards."
Interior Minister Rihards Kozlovskis told Latvian TV it was "clear" there had been a problem meeting building regulations.
Police are also investigating reports that emergency alarms had been set off in the store before the cave-in.
Latvian rescue services spokeswoman Viktorija Sembele said people were being asked to call the mobile phones of relatives feared missing to help rescuers find them in the rubble.
At least 40 people were injured and 33 are being treated in hospital.
TV footage showed rescue workers using mechanical cutters to clear debris from the single-storey concrete and glass building.
The initial collapse happened just before 18:00 (16:00 GMT) on Thursday, when the Maxima store was busy with customers.
Walls and windows also crumbled, leaving the shell of the building piled with rubble, witnesses said.
About 20 minutes later another part of the roof caved in, trapping rescue workers who were trying to reach survivors.Dangerous work
The rescue services believe a total of about 500sq m (5,300sq ft) of roof caved in, according to reports.
Witnesses said customers tried to run out after the first part of the roof collapsed but the supermarket's electronic doors closed, trapping them inside.
Maxima board member Gintaras Jasinskas said 30 employees were in the store at the time, according to AFP news agency.
He was quoted in local media saying he expressed his deep condolences to the families of the victims.
Maxima is a Lithuanian retail chain with shops in all three Baltic states, Russia's Vesti TV news reports.
Leta news agency said the collapse represented the largest loss of life from a disaster since the restoration of independence in 1991, worse than a fire at a nursing home in 2007 that killed 25.
Normunds Plegermanis, deputy head of rescue services, said emergency teams faced difficult conditions at the supermarket.
"Falls are happening from time to time... it is very dangerous to work inside," he said.
Local media said the building, rented by the Maxima chain, had been awarded a national architecture prize when it was completed in 2011.
The reason for the collapse is not known. Some have blamed the weight of soil being used to plant a winter garden on the supermarket's roof.