Health authorities have urged Sydneysiders not to pick up heat-affected or injured bats, warning the animal may carry a deadly virus.

Eight people have been bitten or scratched by bats in Sydney since December 1, according to NSW Health. Another seven have been bitten or scratched in the Hunter New England area this year.

Bats in the Royal Botanic Gardens Sydney. Credit:Jon Reid

The high temperatures harm the bats' health, and several people have tried to free the sick bats that have become entangled in fence wire or netting.

But the bats may carry lyssavirus, which can be transmitted from bats to humans through infected saliva from a bite or scratch, but also if a person gets saliva in their eye, nose or cut in their skin.