The reason for the collapse during shopping rush-hour yesterday was still not known but rescue and police officials said that possible theories include building's design flaws and poor construction work.
Pictures from residential buildings overlooking the store showed an enormous crater-like hole in the roof. Building materials were stacked on remaining sections of the roof, where workers were building a garden as part of the Maxima supermarket's original design plan.
The Fire and Rescue Service said 35 people were injured, 28 of whom were hospitalized, including 10 firefighters. The service could not say how many people might be trapped under the rubble.
She said work was proceeding slowly since both the rubble and remaining sections of roof were like a house of cards and could easily collapse further if a wrong piece is moved or lifted.
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Firefighters suffered casualties when large sections of roof fell on them right after their arrival on the scene.
The rescue service estimated that approximately 500 square meters of roof collapsed, destroying large sections of the store's high walls and nearly all its front windows.
Maxima officials refused to comment and said that they would release a statement later.
The supermarket is located in a densely populated neighborhood between downtown Riga and the city's airport.