A natural gas explosion rocked a Seattle neighbourhood early Wednesday, destroying several businesses and sending nine firefighters to hospital.

Crews were responding to reports of a natural gas leak when the explosion occurred along a main thoroughfare north of downtown, Seattle Fire Department spokeswoman Corey Orvold said.

Seattle Exploson

An aerial view shows the damage from a natural gas explosion that flattened buildings in Seattle Wednesday morning. (Steve Ringman/Seattle Times/Associated Press)

The cause was under investigation. There were no reports of any other injuries or anyone missing. Dogs were being used to go through the rubble just in case.

Video surveillance from the Olive and Grape Mediterranean Restaurant shows a bright flash at 1:43 a.m. and then the room shaking as debris falls from the ceiling. A large garage door covering the restaurant's front windows protected it from extensive damage.

"The Olive and Grape was lucky," owner Paola Kossack told The Associated Press in an email.

Bike shop owner Davey Oil said he arrived soon after the fire trucks.

"There were tons of flames leaping over what was already the rubble of Neptune Coffee, which as you can see now totalled, gone," he said.

Seattle Explosion

A large piece of debris clings to a tree overhead as a firefighter hoses down a still-smouldering building in the rubble left from the early-morning explosion. (Elaine Thompson/Associated Press)

Crews were still dousing the flames with foam as the Greenwood neighbourhood awakened.

Residents were checking out the damage along with the rubble and glass that littered the streets. Workers from one café damaged in the blast poured coffee for firefighters.

Among the businesses damaged or destroyed were Neptune Coffee, Mr. Gyro and the bike shop G&O Family Cyclery. An apartment building and another nearby residential structure were evacuated.

"Our block is a pretty close-knit block and this is pretty terrible," Oil said.

Chocolati Cafe manager Darla Weidman said she was relieved the blast occurred overnight instead of 11 a.m., when the shop sometimes is packed with people.

Mayor offers support

"I know neighbours will do everything they can to support these businesses as they begin the long and challenging task to recover and repair from this incident," Seattle Mayor Ed Murray said in a statement. "The city will also be there to do what we can."

Puget Sound Energy spokeswoman Akiko Oda said gas service for the affected buildings was shut off about an hour after the blast and the shutdown was later expanded.

The utility said it completed leak surveys for the block around the area and found no leaks.

Oda says it will take time to determine what caused the explosion and the utility will be working with the Seattle Fire Department in the investigation.

Pipeline safety investigators from the Washington Utilities and Transportation Commission were also on site.

Seattle Explosion

The Greenwood Space Travel Supply Co., which sells space-themed novelties and toys, is seen across the street from the rubble left by the explosion. (Elaine Thompson/Associated Press)

Firefighters treated for minor injuries

Harborview Medical Center spokeswoman Susan Gregg said eight firefighters and a battalion chief were treated at the facility.

None of the eight men and one woman was admitted to hospital.

"We didn't have anybody with burns, nothing life-threatening, nothing major" said Gregg, adding that some firefighters were checked out because the blast was so powerful that it pushed them back.