(CNN) -- The pilot of a small plane that slammed into a building Thursday morning in Austin, Texas, set his house on fire beforehand and then intentionally crashed the aircraft, a federal official told CNN.

Federal officials told CNN the plane was a Piper Cherokee PA-28 they believe belonged to Joseph Andrew Stack.

Two F-16 fighter jets were sent from Houston as a precaution, but federal authorities said preliminary information did not indicate any terrorist connection to the crash.

"We do not yet know the cause of the plane crash," the Department of Homeland Security said in a release. "At this time, we have no reason to believe there is a nexus to terrorist activity. We continue to gather more information, and are aware there is additional information about the pilot's history.

"At this time, we are referring further questions to local authorities and the FAA."

Read the latest updates on the crash

Two people were transported to University Medical Center Brackenridge, said hospital spokeswoman Matilda Sanchez. She could not provide additional information.

University Medical Center Brackenridge is the only Level 1 trauma center for adults in Austin.

St. David's Medical Center, the other major hospital in the area, said it had not received any patients.

Witnesses described a crash that shook nearby buildings and sent fire and smoke bellowing into the sky.

"I just saw smoke and flames," said CNN iReporter Mike Ernest. "I could not believe what I was seeing. It was just smoke and flames everywhere."

The crash occurred around 10 a.m. (11 a.m. ET).

Firefighters used two ladder trucks and other equipment to hose down the blaze at the Echelon office building, which police said is in the 9400 block of Research Boulevard.

The flames seemed mostly extinguished about 75 minutes later.

The FAA said preliminary information indicated the plane departed Georgetown Municipal Airport north of Austin about 9:40 a.m. CT. An FAA spokeswoman said the plane was Piper Cherokee PA-28.

Jack Lillis, an attendant at Georgetown airport, said initial indications are that the flight originated there but there were conflicting reports and he could not verify that information.

The pilot evidently did not file a flight plan, the FAA said. No flight plan was required because the flight was under visual flight rules, or VFR, because of clear weather.

The Internal Revenue Service in Dallas told CNN the building is a federal IRS center with 199 employees. IRS officials were trying to determine if all the employees were accounted for.