A light plane pilot killed during a takeoff exercise stood no chance of surviving the high-speed crash, a witness said.

The male pilot, aged in his 40s, died on impact when his Lancair 360 crashed in front of horrified onlookers at Bankstown Airport, in Sydney's southwest, about 2.40pm (AEST) today.

Airservices Australia said the pilot was practising "touch and go's" -where the pilot almost lands the plane before taking off again-in the minutes before it crashed.

A spokesman said the pilot did a steep right-hand turn from a height of about 380m before hitting the ground upside down at high speed.

Wreckage from the plane hit at least one other parked aircraft and some runways, which have since been cleared.

Witness and fellow pilot Todd Jackson told Southern Cross Broadcasting the pilot did not stand a chance of surviving the crash.

"I really felt for the gentleman. He had no chance at all, just none at all," Mr Jackson said.

"The first thing I did was ring my wife Susan ... it just prompts you to ring your loved ones."

Mr Jackson said he heard the engine backfire a couple of times before it hit the ground at "a hundred miles an hour" beside a hangar at the airport.

One man had run to the wreckage with a fire extinguisher but there was no fire, he said.

Another witness, identified only as Adam, said there were no apparent problems with the aircraft before take-off.

"I was there when the owner turned up and he apparently witnessed the take-off and saw the undercarriage turn up as per normal and he turned away just thinking it was a normal take-off," Adam said to Macquarie Radio.

"A few minutes later he was told it crashed."

The Airservices Australia spokesman said it was not known if the man was a trainee pilot or why he was practising touch and go's.

"He could have just been testing the aircraft. I don't have any information as to why he was doing that," he said.

A Bankstown Airport spokeswoman said it would conduct a full investigation into the crash.