Rescuers had difficulty searching today for the victims of a crash at a Wichita, Kansas, airport, with investigators fearing the badly damaged building might collapse at any moment.

"We don't like leaving folks who have died in a structure overnight, but we don't want to get anybody else hurt," said Brad Crisp, Wichita's fire marshal.

NTSB waiting to inspect plane in Wichita airport crash. At least 4 dead in small plane crash at Wichita airport. Crews to begin work to recover Wichita plane crash victims.

Four people were killed, including pilot Mark Goldstein, when a Beechcraft King Air 200, full of fuel, lost power in the left engine shortly after takeoff Thursday at the Wichita Mid-Continent Airport.

The plane slammed into the FlightSafety Building, igniting an inferno. Today, small fires were still being put out as pieces of the building continued to break off.

Authorities said today that the three people who were killed on the ground were in flight simulators at the moment of impact. Flight simulator pods typically house a pilot, copilot and flight instructor.

Authorities did not release the names of the three victims. Heavy equipment was expected to be brought in today to help stabilize the building and enable rescuers to recover the bodies.

Five people were hospitalized after the crash Thursday, including one person in serious condition. Goldstein was flying solo.

Goldstein's colleagues today said he knew he was in trouble right away.

"Mark was an air traffic controller and the other other controllers knew his voice," said friend Ron Ryan. "They knew when he declared an emergency and lost the left engine. They knew who it was."

A National Transportation Safety Board team was at the scene of the crash waiting to being its investigation.

ABC News' Ryan Smith, John Bentley and Whitney Lloyd contributed to this story.