While the vehicles on the inner-west Sydney line and Canberra's light rail line are the same model, manufactured by Spanish firm Construcciones y Auxiliar de Ferrocarriles, there is no evidence cracking has been identified in Canberra's vehicles.

An ACT government spokesman said the government was aware of the issue in Sydney and was engaging with the NSW government and Canberra Metro, which operates the Canberra light rail line between Gungahlin and the city.

"Canberra's light rail system undergoes ongoing safety and serviceability checks. This has not identified any issues to date. Canberra Metro will be undertaking regular inspections to check for this issue in addition to the regular maintenance and inspection program already in place," the spokesman said.

"It should be noted that Canberra light rail vehicles operate on a different track type to Sydney light rail and are a much younger fleet."

NSW Transport Minister Rob Stokes said on Friday afternoon the inner-west Sydney light rail line could be out of action for up to 18 months to fix the significant cracking found on all 12 light rail vehicles.

"A lot of countries will be looking at what happens here with keen interest," Mr Stokes said.

He said he was advising global operators to "let them know this same design flaw is likely to be a challenge for their systems as well".

Transport for NSW chief operations officer Howard Collins visited the Lilyfield depot on Friday morning to inspect "and understand what we've discovered", including cracks up to 30cm long on the wheel arches.

He said the trams were not unsafe but "if the cracks propagate further it could be an issue" for the seven-year-old trams, and it will be "no quick fix".

"We want to fill a workshop with these trams with very competent engineers from Australia who can retrofit, strengthen and sort out these cracks permanently," Mr Collins said.

There is a fleet of 14 CAF Urbos 3 light rail vehicles in Canberra, which cost the ACT government about $65 million.

The same light rail vehicles, which are used in Newcastle in Sydney, are operated on light rail networks around the world, including in Scotland, Norway, Brazil, Spain, France and Belgium.

CAF agreed to conduct remediation work on 19 Urbos light rail vehicles in the French city of Besancon after cracks were discovered in the bodies of low-floor vehicles in December 2017, the International Railway Journal reported in January.

The journal also reported similar issues had been found in the same model vehicles in Belgrade.

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The ACT opposition spokesman on transport, Mark Parton, said the ACT government would have known about the potential cracking issue with the vehicles before they were purchased for Canberra, and should explain why they were selected for the city.

"This Labor-Greens government has put all their public transport eggs in one basket, and now it looks like that basket could be about to break," Mr Parton said.

"Canberra could be on the verge of a 18-month shutdown of the light rail, plus further blowouts in the cost of the project."

Plans for key works to allow for the extension of Canberra's light rail to Woden were last week lodged with the National Capital Authority.

The ACT government lodged an application with the authority to raise London Circuit and public consultation for the project has opened.

The plans come after a recent auditor-general report cast doubt on assumptions in the light rail's stage 2A business case.

The report found the government's 2019 business case relied too heavily on so-called "transformational projects" around the transport corridor.

But the government defended the project and said an isolated assessment of stage 2A did not take into account the full benefits of extending the line to Woden, which was the government's intention.

Stage 2A is jointly funded by the ACT and Commonwealth, with the federal government providing $135 million to help build the light rail from Alinga Street.

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