A powerful blast that ripped through a restaurant in northern Japan injured 42 people and caused serious damage to neighbouring buildings, forcing some residents into shelters, officials said.

The explosion in Sapporo on Sunday night started fires and caused the partial collapse of some surrounding buildings.

Images from the scene showed large flames and plumes of smoke rising in the night air, and witnesses described hearing a terrifying boom.

The cause of the blast was still under investigation, police said. One witness reportedly said he had smelled gas after the explosion.

A police official for the Hokkaido region told AFP that despite the large number of injuries, there had been no fatalities.

The Jiji Press agency said one of those injured was seriously hurt, suffering burns to his face, but none of the victims had life-threatening wounds.

Several children were reportedly among those hurt in the explosion.

"I heard a 'bang,' which sounded like thunder, and my condo was shaken," a man in his 50s told The Japan Times.

"There was an enormous sound, 'bang', then when I looked up at the sky it was filled with plumes of smoke," an elderly woman said in footage on public broadcaster NHK.

The two-story wooden building that housed the restaurant, a real estate agency and a clinic was seriously damaged, a Sapporo fire department official told AFP.

The fire from the blast spread to neighbouring buildings, and debris blasted out by the explosion shattered the windows of nearby apartments and restaurants, according to local reports.

"We are investigating details about the damage together with police at the scene," the official said.

National broadcaster NHK said it took firefighters several hours to extinguish the flames, with dozens of vehicles mobilised to deal with the accident.

A 26-year-old female employee at the restaurant jumped from the first floor and broke her leg as she tried to escape the fire, media reports said.

"I'm just relieved that she is alive," her sister, who rushed to the scene, told the Yomiuri Shimbun newspaper.

The blast happened around 8.30 pm (1130 GMT), and the city government opened a shelter to house dozens of people whose homes were damaged.

"The number of evacuees grew to about 60 people around midnight, but now there are 10 people still in the evacuation centre," Sapporo official Yasuhiro Ishizuka told AFP.

The explosion also caused a temporary black-out, with 250 buildings losing electricity, but power was later restored, he said.

Many small and medium-sized older buildings in Japan are built partly or entirely from wood and are vulnerable to fires.

In February, 11 people were killed in Sapporo after a fire broke out at a home for elderly people with financial difficulties.