A subsequent fire caused a building to collapse. The residents reported the smell of gas after the explosion and saw broken windows in the area, reported public service broadcaster NHK.
The explosion cause, 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 on the remains of the building, and trash was scattered over the nearby street.
The explosion also split windows across the street and sent broken glass on the sidewalk, a Twitter user posted.
The fire department in Sapporo told CNN that more than 20 fire trucks were used. The number of reported injuries could increase, Sho Saikoku said in Sapporo fire brigade.
Police and firemen warned of the possibility of another explosion, according to Kyodo local authority.
Sapporo, with nearly 2 million people, is located on Japan’s great northern island of Hokkaido.