Firefighters work on site where a large explosion occurred at a restaurant in Sapporo, Japan, on December 16, 2018.
A subsequent fire caused one building to collapse. Residents reported smelling gas after the explosion and seeing broken windows in the area, public service broadcaster NHK reported.
The cause of the explosion, which occurred around 8:30 p.m. local time, is unknown, and emergency services continue to investigate.
Video shows the blast's destructive aftermath. Firefighters sprayed water onto the building's remnants, and debris was strewn across the nearby street.
The Sapporo fire department told CNN that more than 20 fire engines were deployed. The number of reported injuries could rise, said Sho Saikoku of the Sapporo fire department.
Police and firefighters warned of the possibility of another explosion, according to local news agency, Kyodo.
Sapporo, with almost 2 million people, is on Japan's large northern island of Hokkaido.