Caroline Donnelly was walking along Parramatta Road when she came across the truck.

"I noticed all the activity. It was a truck going along Parramatta Road," she said.

"There's a metal fence [down the middle of the road] and he was avoiding another car and has gone through the steel barrier. There is a lot of spilt oil."

A "Heavy Hazmat" team is onsite laying sand to soak up the oil, she said.

"It looks like the driver is having a cigarette, he looks a little bit shaken."

Two city bound lanes of Parramatta Road remain closed, including the bus lane. Traffic is queued back around two kilometres in each direction.

One westbound lane, which was closed earlier, has now reopened.

 

Transport Management Centre Spokesperson Nicquie Sinclair said traffic in the area is already very heavy and significant delays are expected.

Bus routes 436, 438, 439, 440, 461, 480, 483 and M10 buses are now using Parramatta Road again, but are reporting delays of up to 15 minutes.

Fire and Rescue NSW was called to the site just after 2pm, a spokesman said, adding that the area would be cleared shortly.

"The tank leak has stopped and a Hazmat crew is in attendance. They are going to empty the fuel tank," he said.

"The spill has been treated and they are about to reopen barriers to open the road."