Work has begun on Victoria’s giant suburban rail loop, despite concerns from a major ratings agency about the state’s ability to pay for infrastructure projects.

Geotechnical drilling has begun at Box Hill in Melbourne’s east, as the Andrews government pushes ahead with the Suburban Rail Loop project.

The ambitious 90 kilometre rail link, announced in the lead up to the 2018 state election, would connect every major suburban railway line from Frankston in the southeast to Werribee in the west, via Melbourne Airport.

Premier Daniel Andrews and Public Transport Minister Jacinta Allan visited the drilling site on Tuesday.

“I don’t think you can underestimate just how much this will change the way our city and state works, the way our transportation system operates,” the premier said.

“It is a big project.

“We need more of those sort of infrastructure projects, not the ‘I won’t build it because I won’t get credit for it’ politics of infrastructure, but instead a long-term vision.”

The work will involve drilling boreholes to depths between 30 and 60 metres, with rocks and soil collected to gather information about ground conditions and quality.

Actual project construction isn’t expected to begin until 2022 and could take up to 30 years and $50 billion to complete.

Rating agency Moody’s released a report on Monday cautioning Australian states against rising debt.

It said spending is higher in most states than previously budgeted as governments invest in roads and rail, particularly in NSW and Victoria after state elections.

The report singled out Victoria’s Suburban Rail Loop as a “challenge” to the state’s finances.

But the premier was confident the state would retain its AAA credit rating.

“We are borrowing to build. The real cost and the real pressure comes if we don’t get this infrastructure built,” he said.

“Of course, we are always looking for that balance point – you don’t borrow an unlimited amount of money, you borrow within your capacity to repay.”

Mr Andrews was also hopeful the federal government would help pay for the loop.