A foreign engineer from an Austrian company was killed and two South Korean colleagues were injured Thursday when an unmanned spy drone crashed into their control vehicle during a test flight, police said.

The trio were testing the aircraft for South Korea's military in the western port city of Incheon, police said.

"A 50-year-old foreign engineer from an Austrian company died on the spot when the S-100 drone crashed while they were controlling it remotely from inside the vehicle," a police spokeswoman at Incheon told AFP.

The crash triggered a fire and completely destroyed the 2.5-tonne vehicle, she said.

The 150-kilogram (330-pound) drone and the vehicle were together worth about five billion won ($4.38 million).

"I saw the vehicle, which looked like a large van and was parked in an empty lot, engulfed in flames after the plane circled over our building," an official in a nearby building told AFP.

Two South Koreans were injured but six other people in and around the control vehicle escaped unhurt, the police spokeswoman said, adding the cause was not yet known and government and military officials were investigating.

The nationality of the victim was unclear.

South Korea has used drones to spy on North Korea across the heavily-fortified border. Military authorities confirmed that the S-100 is an unmanned aerial vehicle used for surveillance but declined to disclose details.