DENVER (AP) — Investigators are searching for a man in the rubble of a suburban Denver house that was leveled by an unexplained explosion.
Officials said crews were concentrating Friday on an area where a search dog picked up a scent the day before.
The house in the north Denver suburb of Thornton exploded Thursday. City spokeswoman Lisa Wilson says investigators are looking into whether natural gas was the cause.
Debris clung to surrounding trees and rooftops and was scattered across two square blocks.
Wilson says three people lived in the house and two were at work at the time of the explosion.
Wilson says those two told investigators the third person was probably in the home at the time because his truck and motorcycle were there.
No names have been released.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
Firefighters with cadaver dogs searched into the night for a person believed to be somewhere beneath the smoldering wreckage of a suburban Denver home, as investigators tried to pinpoint what caused the explosion that leveled it and blew out neighbor's windows
The blast on Thursday in Thornton could be heard for miles. Television news footage showed little of the home remained standing, and debris was spread over nearby vehicles and homes as far as a block away.
The two owners of the home told authorities that the car and motorcycle of a third person who lived there were parked nearby, and they feared he was inside, the Denver Post reported.
A dog brought in by the Poudre Fire Authority of Fort Collins picked up a scent amid the rubble late Thursday, fire officials told KMGH-TV. They said earlier that a body had been found but later retracted that statement.
City spokeswoman Lisa Wilson told the Post the response was in "recovery mode."
"The scene is unstable and there are hot spots, and so the investigators have to move very slowly," she said.
Neighbor Robert Lance Russel told KCNC-TV the blast knocked him and his son off their feet at their home across the street. Russel said they called out to see if anyone was in the debris but heard no response.
Todd Branson, who lives behind the home that exploded, said he was watching TV when he heard a boom.
"My back window just blew in, my screen door, the glass just totally blew in. When I had a chance to go out and see my back fence, my back fence was completely gone," he told KUSA-TV.
The explosion caused a fire amid the remains of the house, and it spread to a nearby tree. Residents with garden hoses tried to douse the blaze, which fire crews had under control soon after arriving in the neighborhood about 10 miles north of Denver.
"I was outside talking with my neighbor and it went right up — the insulation and the roof just went up in a big mushroom," Richard Sutton, who lives 1 1/2 blocks away, told the Post.
Thornton Fire Department officials did not return calls for comment. The department's Twitter page said technicians were shoring up the destroyed house in order to improve the search conditions.
Xcel Energy spokeswoman Michelle Aguayo said utility crews were assisting in the investigation, but authorities have not been able to determine whether the explosion was the result of a natural gas leak or another cause.