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A Texas man deliberately crashed a small plane into a building containing a federal tax office Thursday after setting his house on fire.
Two fighter jets were scrambled out of a nearby airport in response to the incident, which an official said does not appear to be linked to terrorism.
"This was apparently - according to an official - a deliberate act," CNN anchor Tony Harris said.
"Joseph Andrew Stack is the name of the pilot."
The plane struck the second floor of the seven story building in Austin, Texas about 10:00 am (1600 GMT) and burst into flames in a massive explosion that forced people to flee out of the windows, witnesses and officials said.
"At this time, we have no reason to believe there is a nexus to terrorist activity," Department of Homeland Security spokesman Matthew Chandler said.
"We continue to gather more information, and are aware there is additional information about the pilot’s history."
North American Aerospace Defense Command (NORAD) launched two F-16 fighter aircraft from Ellington Field in Houston, Texas to conduct an air patrol in response to the crash.
"This response from NORAD is a prudent precaution and consistent with our response to recent similar air incidents," said NORAD spokesperson Jamie Graybeal.
Two people were taken to hospital and one person was unaccounted for, but fire officials said they believed everyone else had been safely evacuated from the building.
"The building shook, it was almost like an earthquake," a witness named Cynthia who was in a neighboring building in the complex told CNN.
Cynthia and her office mates left the building and saw people running towards the building that got hit by the plane.
"People were on the second floor. They couldn't get out. They were hanging out the windows screaming for help."
Luckily there was a truck from a glass company nearby so people grabbed the ladders and were able to help the people get down from the burning building, she said.
One witness named Mike saw the plane crash into the building after noticing that it was flying unusually low.
"I didn't think there was an airport nearby, so I thought it was kind of weird, and saw the plane hit the lower to midsection of the building," he told CNN.
Fire officials who arrived moments later were battling to contain the blaze.
"What they're seeing is heavy fire around the second floor. They've got lots of smoke. Lots of heat. Lots of fire," assistant fire chief Harry Evans, assistant fire chief told reporters.
"The fire continues to burn and they are fighting it. But we are offensive inside the structure."
