The rail bridge connecting Sydney to the Central Coast and Hunter needs urgent repairs on one of its crumbling concrete piers, according to a report handed to the NSW government two years ago.

But Sydney Trains has not repaired the Hawkesbury River bridge, despite being warned of the potentially disastrous risks if work was not conducted within a year.

The Hawkesbury River Bridge, completed in 1945, connects Sydney's Main North Line to the Central Coast. Underwater inspections of the bridge's nine piers are scheduled to take place every six years.

When divers inspected the bridge in 2013, they found major problems with one of the piers. "The downstream pile has a LARGE amount of concrete missing with LOTS of exposed rio bar [reinforcing bar] ... concrete continues to flake off and crumble," said the report, obtained by the state opposition using freedom of information laws.

A subsequent investigation by engineering consultants SMEC​ documented the crumbling concrete and exposed steel at the pier. SMEC's report warned against failing to fix the pier "as the extent of the deteriorated region and the risk of failure of the bridge may increase over time."

And the report recommended repairs "within 1 year, due to the extent of deterioration identified and the potential risk to commuter and freight rail safety".

• Read selected bridge documents here

Those repairs, recommended in November 2013, have not occurred. Labor leader Luke Foley called the situation a "disaster waiting to happen".

"The bridge is quite literally crumbling at its foundations while the Baird government does nothing," Mr Foley said.

"More than 600 train services carrying 11,000 passengers between Sydney and the Central Coast and Hunter use the Hawkesbury River Railway Bridge every day – their safety must be paramount," Mr Foley said.

"The government has known for two years about the potentially devastating risk to commuter and freight rail safety – it needs to stop dragging its feet and start repairs immediately."

Fairfax Media requested comment from the Transport Minister, Andrew Constance, and Sydney Trains. A spokeswoman for Sydney Trains said there was "no danger to customers or freight trains whatsoever".

"The bridge is structurally sound and the report initiated by Sydney Trains helps us plan ongoing maintenance, which is carried out regularly," the spokeswoman said.

The rail operator did issue a tender in 2014 for a contractor to repair the pier, but it did not follow through with it. The spokeswoman said changes to riverbed depth had altered the scope of works required.

"Sydney Trains decided the most responsible approach would be to expand the project and go out to tender again to ensure we still had the best people for the job," she said.

A barge master who lives and works on the Hawkesbury, Bob Brownrigg, said he had not seen any maintenance being carried out on the bridge since divers inspected its foundations in 2013.

Labor's transport spokesman, Ryan Park, last week wrote to the Office of Transport Safety Investigations passing on the material the party had accessed about the bridge.