The water main burst near Audley Street's intersection with Fisher Street just after 11am on Monday.

Footage showed fast-flowing water gushing down Audley and Trafalgar streets.

One person who posted footage online of a car driving through the gushing water described it as the "great flood of Petersham".

Sydney Water and Fire and Rescue NSW crews are on the scene and are trying to turn off the torrent, which is so strong it ripped up sections of the road.

A number of cars parked on the street, which is near Petersham train station, were inundated with water.

Buses are being diverted away from the area, and a NSW Police spokesman said officers had set up road closures on Trafalgar and Gordon streets, Sadlier Crescent, and at Audley Street's intersection with New Canterbury Road.

An employee at The Counter cafe on Audley Street said water was right up to the cafe's doorstep, but had not flooded the business.

He said the water was initially flowing quite quickly, but appeared to be easing just before 1pm.

A Sydney Water spokesman said reports of the incident had first been received at 10.45am and he confirmed that water pressure had been affected in Drummoyne, Rozelle, Ashfield and sections of Leichhardt.

"It may even seem in some circumstances like the water has been shut down, but often if water is coming out of one section of a pipe it can reduce pressure in other sections of the pipe," he said.

"We won't know until they shut it off and start digging down."

He said the cause of the rupture could be anything from tree roots to a change in temperature shifting the ground, which is similar to the way wood can expand and contract with temperature changes.

"We would call it a significant event; we are certainly taking it seriously. We have senior technicians down there now and more crews on the way. But until the water main has been shut off, we won't know the full impact."

Schools in surrounding suburbs have reportedly informed parents that they had no running water, allowing them to collect their children early if they wished.
 

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