A contentious $34.5 million rail line has been promised more federal funding as another gets the green light to open early.

Prime Minister Anthony Albanese joined Victorian Premier Jacinta Allan on a joy ride through Melbourne's Metro Tunnel on Sunday after the project's opening date was shifted forward.

The $15 billion rail line and its five new underground stations were scheduled to open in early December but the date has been changed to November 30 following safety approval.

The prime minister came bearing a celebratory gift, vowing to dig into federal coffer's for the Suburban Rail Loop.

The proposed 90km orbital rail loop is intended to run from Cheltenham in Melbourne's southeast to Werribee in the outer west via the airport at Tullamarine.

So far the Victorian government has co

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