11:30AM EST: [UPDATES IN EXTENDED ARTICLE] Several witnesses have seen a plane crash into near Highway 183 and Loop 360.

The plane crashed into the building at the 9600 block of Research Boulevard around 10 a.m. Witnesses report feeling a tremble, seeing smoke, and seeing the plane hitting the side of the building.

Several witnesses report still seeing explosions after the plane hit. The plane did not leave a smoke trail before hitting the side of the building, according to one witness.

EMS officials said it was a seven-story building and that two people were unaccounted for.

Tucker Thurman was driving to work on the U.S. 183 flyover near MoPac Boulevard (Loop 1) when he said he saw a small plane, very low, flying over the highway. He said he saw it then bank heavily to the right before heading into the building.

“There was a huge fireball. It right into the building,” Thurman said.

EMS officials said they have taken at least two patients to the hospital, but that there are several “walking wounded” at the scene.

UPDATE 11:47AM EST: The police spokeswoman said officials do not yet know whether the aircraft was private or commercial, and they had no immediate word on casualties.

The FBI said there is nothing at this point that indicates that the crash is anything more than an accident at this time.

Initial reports were that the Austin field office of the San Antonio FBI were in the building, but it was later learned that the FBI offices are in a nearby building.

The nearest airport is Austin Bergstrom International Airport, which is some 15 miles away, in southeast Austin, and the crash site is reportedly on the flight path for that airport.

UPDATE 12:40PM EST: An NTSB official told Fox News that they are investigating this as an intentional act, and said it appears the pilot set his own house on fire and then got in his plane and flew it into the building. An NTSB spokesman, however, told FoxNews.com that “we can’t confirm any of that.”

An IRS office is located inside the building, NTSB told Fox News.

UPDATE 1:20PM EST: Authorities said they have identified the pilot as Joseph Andrew Stack. The plane was a small single-engine plane (Piper Cherokee) and took off from an airport in Georgetown, Texas, at 9:40 a.m. and crashed into the building in Austin shortly thereafter. Officials are investigating whether Stack owned the plane or he stole the plane.

DEVELOPING STORY….CHECK BACK FOR UPDATES

(Source: Statesman.com / weareaustin.com / star-telegram.com /Eli Rowe / YWN-32 / YWN-35)