Three North Rocks roads remain closed as crews work to remove asbestos from roads and footpaths.
The Hills Council crews are working with Fire and Rescue NSW to clear the asbestos on Loyalty, Trent and Lenton roads in what is a predominantly industrial area.
PHOTOS: Click here to see photos of today's asbestos removal.
Council's general manager Dave Walker said it appeared asbestos was deliberately thrown off a truck, stretching 300 metres along the road.
"Our crews are working to get this cleaned up as quickly as possible, however they are being very thorough as they clear this toxic waste,” Mr Walker said.
He thanked residents, businesses and motorists for their patience.
"We understand this could be frustrating but unfortunately the precautions are necessary," he said.
Mr Walker said it was unclear how much asbestos had been dumped, but it appeared to be a significant amount.
Council’s place management teams will investigate the incident.
Mr Walker said asbestos dumping was a serious issue.
“Asbestos dumpers are the most inconsiderate and reckless of all illegal rubbish dumpers — they put the long-term health of innocent people at risk," he said.
Individuals caught dumping asbestos can be fined up to $1 million and jailed for seven years. Corporations can be fined $5 million.
■ Anyone with information is urged to call The Hills Council on 9843 0555.