Seattle explosion injures 9 firefighters, wakes residents

Nine firefighters were injured after an explosion leveled several buildings in Seattle early Wednesday, officials said.

The Seattle Fire Department said eight firefighters and a battalion chief were transported to the hospital following the "massive explosion" in the the city's northern neighborhood of Greenwood.

See more reports and pictures from the scene:

At least 17 fire vehicles were at the scene after what one resident described as "an extremely loud boom."

It was not immediately clear what caused the explosion or how the firefighters were injured. NBC News was unable to immediately reach fire officials for more information.

Dozens of residents said on Twitter they had been woken by the blast at around 1:40 a.m. (4:40 a.m. ET).

"It shook the house," 40-year-old Josh Koolbaugh, who lives a couple of hundred feet away, told NBC News by phone. "It sounded like an extremely loud boom."

Koolbaugh, who works for Boeing, walked to the scene after the blast woke him and his wife.

"I saw three buildings that were all leveled," he told NBC News.

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He said at least three buildings had been destroyed: a local coffee shop, a restaurant and a grocery store.

Emily Pfeifer, a 23-year-old graphic designer who lives four blocks away, said she "heard a low boom and was rocked from a dead sleep, like a single gentle shove."

She added: