The state's big-spending budget, unveiled last week, rests on a number of key assumptions about the COVID-19 pandemic, including the arrival of a vaccine and the reopening of international borders in 2021.

The federal government says it's on track to start vaccinating people against the virus from March, but Mr Pallas doesn't believe a vaccine will be widely available until the end of next year.

"I am very confident that we will get to a broadly available vaccine, but it won't be the sort of early arrival that the optimists seem to think," he told parliament's public accounts and estimates committee on Tuesday.

"Given the developments that are occurring through the three principal frontrunners for the provision of vaccine, we will see it become available in the second half of next year and it will be broadly applicable by the end of the year."

He said without a vaccine the state's economy would operate at a "COVID-normal", with a number of restrictions remaining in place.

Treasury Secretary David Martine said it was unlikely international travel would return to pre-pandemic levels until a vaccine becomes globally available.

"That's going to take some time. I'm not expecting large movements of people across international borders until well into the next calendar year," he said.

Mr Martine conceded it was unlikely international students will return to the state until the start of 2022.

International education has been Victoria's largest services export industry for more than a decade, generating $13.7 billion in revenue in 2019 and employing almost 80,000 people.

Victoria hosts about a third of Australia's international students.

It comes as the first charter flight of international students touched down in Darwin on Monday as part of a pilot program to bring students back to Australia.

Two similar programs in Adelaide and Canberra were put on hold due to the second wave of the pandemic in June.

The budget is intended to fast-track the state's recovery out of the coronavirus crisis and includes about $80 billion in infrastructure spending and $49 billion in new stimulus measures.

As a result, debt is expected to soar to $154.8 billion by 2023/4 - about 28.9 per cent of the size of Victoria's gross state product.

International credit agencies are wary about the state's record level of debt, with S&P warning there's a "one-in-two likelihood that we will lower our rating on Victoria".

The treasurer said the government was putting the interests of Victorians "first and foremost".

"Whether or not we keep a AAA credit rating is beyond my control. But we will continue to manage our budget in a AAA-rated responsible approach," Mr Pallas said.

Interest will increase between $1.9 million and $10 million per year if Victoria's credit rating was to drop to the second-highest level of AA+.

"The rates are incredibly low at the moment and the spreads are even lower," Mr Martine said.

Australian Associated Press