An explosion near a pub in the northern Japanese city of Sapporo on Sunday night injured at least 42 people, including one critically, said Hokkaido Police public relations officer Ryohei Kashihara.
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 explosion also shattered windows across the street, sending broken glass onto the sidewalk, a Twitter user posted.
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.