An explosion at a restaurant in northern Japan injured 42 people late Sunday, police said, and caused surrounding buildings to collapse.

Fires broke out following the blast in the northern city of Sapporo, Kyodo news agency said, and images from the scene showed large flames and plumes of smoke.

The cause of the blast is being investigated. One witness said he had smelled gas after the explosion.

The building that housed the restaurant was heavily damaged, as were other nearby businesses, Jiji news agency said.

Children were injured in the blast, Jiji added, citing police.

National broadcaster NHK said it took firefighters several hours to extinguish the flames.

Police warned earlier of possible secondary explosions, according to Kyodo, which described buildings collapsing following the incident around 8.30 pm.

– with reporting by Agence France-Presse