KENOSHA — A helicopter crashed through the roof of a house in southeast Wisconsin on Sunday, killing the two people on board but leaving the family inside the house unharmed.

Five people were in the house when the helicopter crashed at about 5:30 a.m. Sunday about one mile south of the Kenosha Airport, said police Sgt. Eric Larsen.

The Federal Aviation Administration and the National Transportation Safety Board were just starting to investigate the crash, FAA spokesman Tony Molinaro said. Molinaro said he was unable to provide details or a possible cause of the crash. The names of those killed were not immediately released.

Weather officials reported some fog in the area at the time, but it was not known if that played a role in the crash. The National Weather Service said that at 5 a.m., visibility at the Kenosha Airport was about half a mile. Visibility had improved to about three-quarters of a mile to a mile by 5:30 a.m., meteorologist Chris Franks said.

Gary Stielow, who lives about 100 yards from the crash site, said he woke up and heard the helicopter sputtering before it crashed.

"The engine just didn't sound right," Stielow said. "It was sputtering. It was at full power, but it was sputtering real bad. Then you just heard a loud boom."

Stielow said he ran outside and saw the family had made it safely out of the house. The bodies of the two people killed in the crash were on the ground next to the helicopter's engine, which was on fire, Stielow said.

The helicopter was a 2006 Robinson R44 registered to Midwestern Air Services, of Kenosha, a company that offers charter services and flight training. A phone listing for the firm's owner could not immediately be found.

The airport's tower does not open until 7 a.m., so travel earlier than that is "at your own risk," said Corey Reed, operations supervisor at the airport.

The helicopter didn't have a flight plan on file, Reed said.

Ed Malinowski, an air safety inspector for the National Transportation Safety Board, said a preliminary report on the crash will take about a week to complete.

Malinowski said he didn't think the helicopter had a black box, which could have recorded the aircraft's operating conditions at the time of the crash.