TOKYO－Japanese police were on Monday investigating the cause of a powerful blast that ripped through a restaurant in the country's northernmost Hokkaido prefecture, injuring 42 people and damaging surrounding buildings.

The explosion in the city of Sapporo on Sunday night started fires and caused the partial collapse of some neighboring buildings, forcing dozens of residents into shelters, officials said.

The cause of the blast was still under investigation, police said, but there were reports that it may have been a gas leak.

Some reports said fumes were leaking from spray cans that had been collected for disposal at a real estate company in the building.

But investigators were also looking into at least nine propane tanks installed in the building for the various businesses located inside.

Numerous customers at the restaurant on the building's first floor said they smelled gas at the time of the explosion, Kyodo News reported.

The blast produced large flames and sent plumes of smoke rising in the night air, with witnesses describing a terrifying boom.

The two-story wooden building, which also housed a clinic, was seriously damaged, said a Sapporo fire department official.

Police said 42 people had been injured, but there were no fatalities. Among the injured were several children, as well as a man who suffered burns and a woman who jumped from the building to escape, breaking her leg in the process.

"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 ceiling fell, then the entire second floor collapsed and we were all stuck. We managed to escape after everyone kicked through the wall," a person who was in the restaurant at the time told Kyodo.

The fire spread to neighboring 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 fire department official said.

The blast happened around 8:30 pm, and the city government opened a shelter to house dozens of people whose homes were damaged.

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

The three tenants in the building were poorly prepared for possible fires, the fire department said.

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

AFP - AP - XINHUA