BEND, Ore. -

A northwest Bend neighbor was rocked awake early Thursday by an explosion and fire that severely burned one man. Investigators spent the day on scene and determined the blast apparently was sparked by someone lighting a cigarette in a cottage living room, near a furnace with a loose natural gas connection.

The explosion occurred and fire began in the living room of a more than 50-year-old, 240-square-foot cottage built behind the larger, main home at 337 1/2 NW Georgia Avenue, said Deputy Fire Marshal Susie Maniscalco.

?The violent explosion occurred when the occupant of the cottage attempted to light a cigarette,? Maniscalco said in a news release. ?Evidence indicates that the connection of the furnace to the natural gas line was not connected tightly.?

The homeowner believed the cottage had a smoke alarm, but did not have a carbon monoxide alarm, she added.

Two adjacent homes had relatively minor exterior damage from the fire. The critically injured man, identified as Michael Flint, was taken to St. Charles Medical Center-Bend, then flown to the Oregon Burn Center at Legacy Emanuel Medical Center, where a spokesman said he remained in critical condition Thursday evening.

At least 15 people called Deschutes County 911 dispatchers to report the blast shortly before 4 a.m. in the Old Town neighborhood, just south of downtown Bend.

"It was just a concussive explosion," said Mike King, who lives next door to the house that exploded.

Fire crews arrived to find the cottage "well-involved" and two larger, neighboring homes beginning to catch fire, as well as several trees, said Battalion Chief Dave Howe.

"One firefighter who lives in the neighborhood told me it was not so much that he heard it, but he felt it -- rattled their windows, woke everybody up," Howe told NewsChannel 21. It was a fairly significant explosion."

King added, "We saw it jumping into the trees and the house behind the fence line."

Firefighters extinguished the flames that were towering over the homes and, once out, began investigating the cause of the fire, Howe said.

Every available unit in Bend responded to the fire scene. Redmond fire crews were called in on mutual aid to help cover the district while about 20 Bend firefighters worked at the location.

Several homes were evacuated, but the fire was under control by about 5 a.m.

Several Cascade Natural Gas trucks lined the adjoining road as investigators dug through the severely damaged cottage.

Deschutes County property tax records show Dan and Martha Mahoney of Bend own the property, while Ryan O'Toole was listed as the renter.

Losses were estimated at $26,000 to the cottage, $30,000 to the home at 337 NW Georgia Ave. and $15,500 to the home at 334 NW Hunter place.

The American Red Cross was called in to help and said two people lived in the cottage, and a dog was missing at the time. The agency provides, food, clothing, comfort kits and other aid, and lodging as needed.

But in one happy element of the tragic story, the missing dog, a black lab named Paris, was found hiding about a half-block away, between two houses, scared but otherwise unhurt.

Howe said she was "safe and sound with her owner. She was freaked out but she is a very nice girl."