Shocked air show spectators have been sent home as investigators probe a small plane crash that has left a pilot fighting for life.
The pilot was attempting an aerobatic manoeuvre during a solo demonstration at the Avalon Airshow on Friday afternoon when the aircraft lost control and crashed into the ground.
Andrew, a witness who did not give his surname and was watching the display with his family, said the plane came down in a loop and could not recover.
"We're OK ... everyone was a bit stunned," he told AAP.
Another witness said the aircraft was diving and flattened out before the right-hand wing dipped and it rolled.
"The exact circumstance surrounding the crash are yet to be determined," police said.
The crumpled wreck of the orange plane came to a stop near the tarmac and sparked a small grass fire.
The pilot, who was the sole occupant, suffered serious injuries to his upper and lower body.
He was flown to Melbourne's Alfred Hospital in a critical condition, Ambulance Victoria confirmed.
No one else was injured as the crash occurred a long way from crowds near the tarmac and in the grandstand.
The crash is believed to have occurred during a solo aerobatic display hosted by a NSW event management company.
It featured the Wolf Pitts Pro, an aircraft with a top speed of 414km/h and the ability to withstand large G-forces.
The Australian Transport Safety Bureau has launched an official probe, with a team of investigators on their way from Canberra.
They will examine the site and wreckage and recover any aircraft components for further examination.
"Investigators will also seek to interview any involved parties, and collect relevant recorded information including available flight tracking data, as well as pilot and aircraft maintenance records, and weather information," the bureau's chief commissioner Angus Mitchell said.
Anyone with video footage of the aircraft at any phase of the flight, or in the immediate aftermath of the crash, has been urged to contact the bureau.
Almost 250,000 spectators were expected to flock through the gates of the airport, between Melbourne and Geelong, for the biennial air show from Friday to Sunday.
The rest of the day's events were cancelled, with security ushering patrons from the airport.
The decision was made to allow the bureau's investigation team full access to the site, Avalon Airshow organiser Justin Giddings said.
"Our thoughts are with the pilot and his family, friends and team members," he said.
Organisers are preparing for the event to resume on Saturday morning, pending confirmation.
