RIGA, Latvia — Latvia's Prime Minister Valdis Dombrovskis resigned Tuesday after accepting political responsibility for the collapse of a supermarket roof in the capital that killed 54 people and wounded at least 40 others.

Dombrovskis' decision means that his center-right government automatically falls. He is the longest serving prime minister in Latvia's history.

Last week's collapse of the Maxima supermarket was the worst disaster since Latvia declared its independence from Soviet Union in 1991, and has caused a storm of outrage from Latvians.

Police have opened a criminal investigation into the cause of last week's tragedy. Possible explanations for the disaster include a flawed design, substandard construction materials, and corruption.

President Andris Berzins can either reject the resignation or accept it and nominate an acting prime minister whose job it will be to form a new cabinet.

Dombrovskis came to power in 2009 as Latvia's economy was sinking into a deep recession and was charged with leading harsh budget cuts and tax increases while at the same time implementing tough structural reforms demanded by international organizations such as the International Monetary Fund.

Dombrovskis was re-appointed twice as prime minister since then, and is widely credited with preventing the small Baltic nation from going bankrupt.