More than 40 people have been injured in an explosion at a restaurant in Sapporo, northern Japan.

Police said one person was in a serious condition while another 40 suffered mild injuries in the blast in the capital city of Japan’s northern main island Hokkaido.

They are being treated at nearby hospitals.

Television footage showed the restaurant in flames. The cause of the explosion is being investigated.

Japan Explosion
Dozens of people were injured in the explosion (Kyodo News via AP)

The explosion happened at a restaurant in Sapporo’s Toyohira district.

The footage later showed grey smoke billowing from the restaurant as dozens of firefighters poured water on to the building, which was charred and nearly collapsing.

Japan Explosion
The explosion caused nearby apartment buildings and houses to shake (Kyodo News via AP)

Windows in a block of flats next door were broken, and cars parked outside were partially covered with debris that had fallen on them.

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