A flying fox soars above the trees in the Royal Botanic Gardens in Sydney. File picture: Mark Baker/AP

Sydney - People were warned to be alert for bat attacks in the region north of the Australian city of Sydney on Monday as soaring temperatures caused stressed bats to bite and scratch.

Health officials said people in the Hunter Valley and New England region north reported an unprecedented number of bat attacks on people, the national broadcaster ABC reported.

Two of the attacks were by bats or flying foxes infected with a virus similar to rabies, the ABC reported.

Public health physician David Durrheim said there had been seven attacks in the past two weeks, higher than ever seen before.

"Two of the bats submitted for testing have actually had lyssavirus infection, so it is a real concern for us and those people who have been exposed," Durrheim told the ABC.

He said the unusually hot weather, with temperatures regularly in the 40s, had caused bats to suffer ill health and be disorientated, falling from trees and getting caught in wires.

"People trying to assist them have unfortunately got scratched or bitten."

Black flying foxes, or bats as they are commonly called, start dying when it reaches 42 degrees Celsius. Grey headed flying foxes die when it hits 43 degrees.

Many bats carry the rabies-like Australian bat lyssavirus, which can be deadly to humans. Durrheim said once it starts in the human body it can't be effectively treated.

"Almost everyone dies," Durrheim told the ABC.

Fiona McBurney from the animal rescue group Wildlife Aid said experts should be called in when people see bats in distress.

"Our bat carers are immunised and trained to handle these bats," she said.