An asbestos spill had authorities on their toes in Sydney over the weekend.

They were called out to attend to a spill in the suburb of Old Guildford in Sydney's west.

Reports say a truck accidentally dumped up to two tonnes of old building materials including asbestos.

The cancer-causing material was found amid the pile left late on Sunday night.

Authorities originally thought it had been an intentional dumping, not uncommon when companies want to avoid proper disposal fees, but are now considering the spill an accident.

Fire crews spent the night clearing up the mound of material, taking extra precautions against the dangers of asbestos.

Fire-fighters wore protective clothing and doused the waste with water to stop any fibres becoming airborne. They mess was then covered it with black plastic before it could be removed.

Residents have told Macquarie Radio reporters that they saw a truck driving down Springfield Street in Old Guildford around the time of the spill.