The aircraft came down in rugged bushland and plunged off a cliff face on a day when a severe weather warning was in place and Australia's largest city grapples with what is forecast to be its wettest July in 52 years.

"A helicopter crashed in bushland. At this stage we can only confirm two dead, hopefully there are not more," said Acting Superintendent Michael Banfield, adding that they were still trying to track down the owners of the chopper.

The Australian Transport Safety Bureau said the helicopter involved was a Bell 206, which typically seats between five and seven people, including the pilot.

"The helicopter is a complete wreck," added Banfield.

"A number of witnesses said they saw a part fly off the back off the helicopter but I can't confirm that right now."

A witness told local radio he heard the helicopter flying very low and feared it was going to crash into a tennis and netball court complex in the area.

"I thought the helicopter was going to crash into the roof, but it went into the bush," he said.

"There's smoke coming up."

The crash came on a day of wild weather, with the local State Emergency Service receiving 560 calls for help in the 24 hours to Friday morning, with Sydney drenched by more than 80 millimetres (three inches) of rain.

Copyright AFP (Agence France-Presse), 2011

Copyright APP (Associated Press of Pakistan), 2011