First responders work at the scene of an explosion in Sapporo, Japan, Sunday, Dec. 16, 2018. Dozens of people were injured in the explosion Sunday night at a Japanese restaurant in northern Japan, police said. The explosion occurred in Sapporo, the capital city of Japan's northern main island of Hokkaido, and caused nearby apartment buildings and houses to shake. (Kyodo News via AP)

First responders work at the scene of an explosion in Sapporo, Japan, Sunday, Dec. 16, 2018. Dozens of people were injured in the explosion Sunday night at a Japanese restaurant in northern Japan, police said. The explosion occurred in Sapporo, the capital city of Japan's northern main island of Hokkaido, and caused nearby apartment buildings and houses to shake. (Kyodo News via AP)

TOKYO (AP) — A suspected gas explosion destroyed wooden buildings housing a restaurant and a real estate office in northern Japan on Sunday night, injuring 42 people, police and local media said.

The powerful explosion in Sapporo, the capital city of Japan’s northern main island of Hokkaido, shook nearby buildings, shattered windows and scattered wooden debris across the area. Some residents told reporters they thought the blast was an earthquake.

One person was in serious condition, but police said the other injuries were mostly mild.

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Police are investigating the cause of the explosion in Sapporo’s Toyohira district. Kyodo news agency reported that a gas safety center official noted five propane gas tanks outside of the pub and two outside the real estate office.

The fire burned for nearly six hours, Kyodo said, and photographs and TV footage showed smoke rising above charred, collapsed debris as dozens of firefighters poured water onto the building. Windows on an apartment building 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. It said neighbors were being provided shelter overnight.