A small twin-engine plane crashed into a building Thursday morning at Mid-Continent Airport in Wichita, Kansas.

ABC News reports that emergency crews arrived on the scene at Mid-Continent Airport, and two people were found to have died, while five other people were rushed to a local hospital with "serious" injuries, Wichita Fire Department Chief Ron Blackwell confirmed.

Blackwell said officials don't know what caused the incident.

Responders battled a "horrific firefight for several minutes" according to Blackwell.

KFSM reports that the plane was flying to Mena, Arkansas.

A federal official confirmed to ABC News that the situation is not terrorism related.

The twin-engine Beechcraft King Air hit the top of the Flight Safety Building shortly before 10 a.m. after losing power in one of its engines soon after its departure from the Mid-Continent Airport on Thursday, according to the Federal Aviation Administration. Approximately 100 people were inside the building at the time.

It is believed the Beechcraft King Air struck the building as it attempted to return to the runway.

"There wasn't a loud bang, there wasn't a loud pop. It just sounded like something falling off a truck," Jaison Podkanowicz, who works near the airport, told NBC News.

Podkanowicz added that he saw the airplane sitting on the top of the building on fire while black smoke hung in the air.

Four people are now missing, according to NBC. Blackwell said only the pilot was found inside the airplane. The two people confirmed dead were discovered inside the building.

A search for the missing people was delayed after part of the building collapsed, making it too dangerous for search crews to go inside.

FAA investigators were on scene. The National Transportation Safety Board was notified of the plane crash.

Mid-Continent Airport is a commercial airport about 7 miles west of downtown Wichita. It is the largest and busiest airport in Kansas.