NSW Fire and Rescue has not found anyone trapped under a wall that collapsed in Sydney's south earlier today.

Four storeys of scaffolding collapsed on a row of parked cars during demolition works on a building at Bexley shortly after 8:00am, and fire crews received reports of one person trapped.

A crane was used to stabilise the wreckage and firefighters are continuing to search the rubble.

"A passer-by stated that they believe someone was trapped under the rubble," Superintendent Tom Cooper said.

The wall brought down powerlines and crushed three vehicles next to a petrol station on Frederick Street.