A gas company employee, who had gone to check on the leak Tuesday night, was critically hurt with second- and third-degree burns, the police department said. He was airlifted to a hospital.
The hotel in the Seattle suburb was evacuated before Tuesday night's explosion, Police Chief Steve Strachan said.
Three people believed to have been staying at the hotel were unaccounted for Wednesday morning, according to John Hawkins of the Bremerton Fire Department.
But, by Wednesday evening, that was no longer the case.
"There is no evidence that the people who had originally been unaccounted for were at the hotel at the time," Bremerton Fire Chief Al Duke said. "Cadaver dogs have been through the hotel several times, and we are pretty confident there was no one in there."
'It looks like half our hotel's blown up'
Hotel staff called the fire department to report the smell of natural gas, then immediately began evacuating guests, Strachan said.
Firefighters and the gas company arrived to check for a gas leak. While they searched, the gas ignited, blowing the firefighters back, the police department said.
The leak was at the east end of the hotel, where there were guest rooms.
The explosion sent up a plume of black smoke, and residents took to social media to say they could feel the shaking from the blast from miles away.
"Making dinner and heard a loud boom and our entire house shook," Emily Sardar tweeted from near Port Orchard, Washington.
Jeff Jackson and his wife were visiting from Australia. They checked into the motel, then went out for dinner. From the restaurant, they could see thick black smoke rising.
"We've come back, and it looks like half our hotel's blown up," he told CNN affiliate KOMO