Updated – Nov. 22, 12:22 p.m., ET
It is unclear what caused the roof to collapse, although a roof garden was being constructed at the time of the accident. Witnesses say when the first part of the roof collapsed, shoppers tried to escape, but the electronic doors trapped them inside.
Prime Minister Valdis Dombrovskis visited the scene, and said, "The police have started the investigation already. The criminal process has started about violating building standards."
The supermarket was part of the Maxima retail chain, and local media have reported that the store was awarded a national architecture prize when building was completed in 2011, however, Interior Minister Rihards Kozlovskis has told Latvian TV it's "clear" that the building had problems meeting building regulations.
Rescue efforts have been ongoing since the collapse occurred at 6 p.m. local time. Three rescue workers and eight firefighters are reported to have died while trying to rescue those trapped inside the rubble. It's reported 60 soldiers are on the scene.
Latvia's government has declared three days of mourning starting Saturday.