At least 42 people injured as a blast occurred in a restaurant in northern Japan's Sapporo city. The cause of the explosion is not known.

Firefighters operate at the site where a large explosion occurred at a restaurant in Sapporo, Hokkaido, northern Japan, in this photo taken by Kyodo December 16, 2018. Mandatory credit Kyodo
Firefighters operate at the site where a large explosion occurred at a restaurant in Sapporo, Hokkaido, northern Japan, in this photo taken by Kyodo December 16, 2018. Mandatory credit Kyodo (Reuters)

Japanese police say more than 40 people have been injured in an explosion at a restaurant in northern Japan.

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

Police say 42 people were injured, most of them mildly, though one is in serious condition. They are being treated at nearby hospitals.

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.

Police and firefighters worked to get the site under control, fighting flames and smoke, and warned people in the neighbourhood of the possibility of another explosion, the agency reported.

The footage later 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, and cars parked outside were partially covered with debris that had fallen on them.

"I heard a bang which sounded like thunder, and my condo was shaken," a man who lives nearby was quoted as saying by the Japan Times. 

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

A witness told NHK that he smelled gas after the sound of an explosion. The broadcaster said the district office was to set up a shelter for neighbors of the restaurant to stay overnight so they could escape the smoke.

An earthquake earlier in September this year had caused an island-wide blackout that lasted two days and killed at least 21 people.

Source: AP