'Pigs fly': Metro deadline delays cloud opening date

Doubts are growing over Melbourne's much-hyped Metro Tunnel opening to passengers in 2025 after key contract deadlines were pushed back.

A contract variation tabled in Victorian parliament on Thursday pushes back the provisional handover of infrastructure to operators to April 30.

That is 12 months later than planned three years ago.

Final acceptance of the tunnels and stations has also been delayed from March 17 to as late as New Year's Eve 2025.

A 2018 document shows the original construction at Melbourne's Metro tunnel, with final acceptance due exactly one year later.

In 2021, the provisional date was revised to April 30, 2024 and final acceptance moved to March 17, 2025.

Opposition transport infrastructure spokesman David Southwick suggested the state Labor government had repeatedly moved the goalposts, casting doubt over the project's 2025 open date.

"If you believe that one, well pigs fly," he told reporters at state parliament.

"This government just keeps pushing the envelop, rolling things back and ultimately Victorians end up paying for it.

"It's an absolute disgrace."

The mega project was originally costed at $10.9 billion when it was first announced in the 2016 budget.

The price tag for taxpayers has grown to $13.48 billion after an $837 million blowout was confirmed in September, including $745 million in additional payments if builders meet the new delivery timelines.

It will connect the busy Sunbury, Cranbourne and Pakenham lines through twin 9km tunnels under the city.

Major construction on three of the five new underground stations at Anzac, Town Hall, State Library, Parkville and Arden has wrapped up and test trains are running through the tunnels.

Transport Infrastructure Minister Danny Pearson said the network remained on track to open in 2025 but refused to guarantee it, citing potential "external factors".

"I don't have a crystal ball," he said.

"Nobody could have foreseen COVID ... but that's what happened.

"I'm confident that we'll have people riding on the Metro Tunnel in 2025."

An exact opening date has not been set.