The building collapsed on Tuesday afternoon in Nyagatare, some 100km north-east of the capital Kigali, and rescuers were scrabbling to find survivors, police said.
"We think between 30 to 50 people were working on the building when it collapsed. We are continuing our rescue operations now," police spokesperson Theos Badege said.
A further 21 were injured and were being treated in hospital, police said in a statement.
The Rwanda Defence Forces and the police had secured the site and were coordinating the rescue operation, police said.
The town is the largest in the north-eastern region, sandwiched between Rwanda's border with Uganda and Tanzanianear the Akagera National Park.
Police said they were unable to establish the cause of the building's collapse, but this would be subject to an investigation by local and national authorities once the rescue operation were concluded. – Reuters