Services on Sydney’s inner west light rail will be suspended for at least a month due to the extent of cracks found in all 12 tram sets which operate on the line from the city centre to Dulwich Hill.

Transport Minister Rob Stokes also told a budget estimates hearing on Tuesday that an investigation by the state’s Office of Transport Safety Investigations into the cracked trams will begin shortly.

“We’ll be asking them also to undertake a review into this incident. I’m obviously concerned because it affects the entirety of the fleet,” he said.

The inner west light rail line will be closed for at least another month.CREDIT:CHRISTOPHER PEARCE

Tram services were suspended on the light rail line on Thursday after cracks were discovered during routine maintenance inspections.

Under questioning from Labor MLC Daniel Mookhey, Mr Stokes said it was “obviously a concern” when route maintenance had uncovered a problem with the entire inner west tram fleet.

“We will hold Transdev to their contractual obligations,” he said of the private operator of the line.

Transport Minister Rob Stokes.CREDIT:LOUISE KENNERLEY

Significant cracks were discovered in the bogey box body – otherwise known as the wheel arch – of the trams after the floors of the vehicles were removed. It came after inspections in early October uncovered cracks in other areas of the trams which are more easily fixed.

Transport for NSW secretary Rob Sharp said the timing of a return to full service on the 12.8-kilometre line would depend on feedback from engineers due later this week.

But he said there was enough evidence to indicate that the transport agency “shouldn’t be rushing” to press some trams back into service, and it was adopting a cautious approach.