WICHITA, Kansas (REUTERS) - A small plane crashed into a building at Mid-Continent Airport in Wichita, Kansas, on Thursday morning, killing at least four people and injuring five and setting off an explosion and fire, officials said.

The two confirmed dead were believed to be in the flight safety building when the plane hit and at least five people were unaccounted for, Wichita fire chief Ron Blackwell told a news conference.

"Firefighters engaged in a horrific firefight for several minutes and now we have the fire under control," Blackwell said.

Television video showed heavy, dark smoke coming from the building after the crash. There were more than 100 people in the building at the time of the crash.

One person was in critical condition and three in fair condition at Via Christi St Francis Hospital, spokeswoman Maria Loving said.

One more person was en route, she said.

The pilot of the plane, which was identified as a twin-engine turbo-prop Beechcraft King Air 200, reported losing engine power just after taking off from the airport and crashed as it tried to return, the Federal Aviation Administration said.

The pilot was believed to be the only person in the plane, said Roger Xanders, chief of airport police and fire. He said authorities had not determined the owner of the plane.

Blackwell said the plane appeared to strike the top of the building and the fire got inside the building.

The building sustained serious damage, including the collapse of walls and ceilings, the airport said on Twitter. The commercial airport remained open.

The National Transportation Safety Board will lead the investigation, the FAA said.