TOKYO — More than 40 people were injured in an explosion Sunday night at a restaurant in northern Japan, police said.

The explosion occurred in Sapporo, the capital city of Japan's northern main island of Hokkaido.

Police said 41 people were injured, most of them mildly, though one was in serious condition. They were rushed to nearby hospitals for treatment.

The cause of the explosion, which occurred at a two-story restaurant in Sapporo's Toyohira district, is under investigation, police said, adding that they had no further details.

TV footage from Japanese public broadcaster NHK showed the restaurant in flames, with debris scattered on the ground.

The footage showed gray smoke billowing from the restaurant as dozens of firefighters poured water onto the building, which was charred and nearly collapsing. Windows on an apartment building next door were broken.

A witness told NHK that he smelled gas after the sound of an explosion.