Three dead after two light planes collide in Sydney

Three men have died after two light planes collided and crashed into bushland in Sydney's south-west this morning.

The collision Jabiru and Cessna 182 prompted a major emergency response in the vicinity of Belimbla Park near Oakdale before midday.

Two men died on board one plane, while a pilot lost his life in the second aircraft.

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The aircraft fell into the back of a rural property with debris strewn among the trees.

Locals ran to the scene to help but were unable to access the site as fire had broken out in the scrub.

The Rural Fire Service worked to contain the flames before crews could reach the wreckages.

"We just heard a big bang and then we saw a lot of big black smoke coming from the back of our property," resident Natasha Xuereb said.

"It's really frightening to know that it's just happened right at the back here and we feel helpless too."

Police set up two crime scenes and members of the public were urged to avoid the area.

An investigation into the cause of the crash will be undertaken by the Australian Transport Safety Bureau.

"A team of transport safety investigators from the ATSB's Canberra office, with experience in aircraft operations and maintenance, is preparing to deploy to the accident sites of both aircraft to begin evidence-collecting activities," the investigator said in a statement.

"Over coming days, investigators will undertake site mapping, examine the wreckage of both aircraft, and recover any relevant components for further examination at the ATSB's technical facilities in Canberra."