A swath of Sapporo City, the capital city of Japan's main northern island of Hokkaido, was covered with smoke, shattered glass and collapsed debris in the aftermath of a suspected gas explosion, Japanese public broadcaster NHK reported.
Most of the injuries were minor, but at least one person was in serious condition, according to the report.
Flames still were smoldering among the wreckage of the two-story wooden building around 1 a.m. Monday local time, nearly five hours after the explosion occurred, NHK and other local media outlets reported.
The building, a pub on one floor and a real estate office on the other, was destroyed.
Authorities suspect gas leaking from more than 100 deodorizer spray cans in the building, which may have been intended for disposal, caught fire, local media outlet Kyodo News reported.
Some witnesses said the blast felt like an earthquake.
"Dawn and a tremendous explosion sounded from two taverns nearby," a witness told NHK. "The explosion broke the window glass of the shop where I worked. It seems there are many injured people on site."
"I felt that it rocked as much as in the September earthquake," another witness said.