At least 45 people have been killed when the roof of a supermarket collapsed in the Latvian capital, Riga. Rescue efforts are continuing and police have launched a criminal investigation. Three of those killed were emergency workers who were helping people trapped, when more of the roof came down. The number of deaths makes this the former Soviet republic's worst disaster since the country became independent in 1991. Police say they expect the number to rise further. It is unclear how many more people could still be inside.