A gas explosion at an apartment building outside of Moscow Monday left five people dead and injured six others, police said. The explosion occurred inside a nine-story apartment building in the village of Sergiev Posad, RIA Novosti reported. Police said it was caused by a gas leak. Eight apartments on the building's top two floors were completely destroyed and some apartments on the seventh floor were damaged, the Emergencies Ministry said. A total of 350 people were inside the building at the time of the explosion. Police said they were searching the building Monday to make sure no one remained trapped inside.