A high-speed rail link between Geelong and Melbourne is being considered by the Victorian government, with $50 million set aside in next month's budget to examine a rail pathway to Melbourne Airport.

The initial planning work will investigate a preferred option, including the possible electrification along the existing rail corridor.

It will also explore a new dedicated high speed rail alignments and a new fleet of trains capable of travelling up to 300km/h.

"This vital work will help determine the best way to deliver high-speed rail to Geelong as part of the Melbourne Airport Link," Public Transport Minister Jacinta Allan said on Thursday.

"This is about ensuring any link to the airport delivers better services for Geelong and regional Victoria."

The Victorian government wants a future Melbourne Airport Link that fits into the existing rail network, to serve the growing western and northern suburbs and provide better services for regional areas.

It says the announcement complements work it is already doing with the Commonwealth on a preliminary business case on a Melbourne Airport rail link.

Earlier this month, Prime Minister Malcolm Turnbull pledged $5 billion from the Commonwealth to help build the link.

There are four potential routes, but Canberra's proposed path through Maribyrnong is not the premier's preferred option.

Premier Daniel Andrews said on Tuesday that the Sunshine route, or Ballarat as the next order of priority, are the best paths for the airport rail link.

Mr Andrews said the government will continue its planning working with the Commonwealth, with work due in coming months.

However, he also said clarity was needed about Mr Turnbull's pledge to provide "equity funding".

"I'm not entirely sure what that means. But it'd be unprecedented for a Commonwealth government, rather than granting funding, to provide equity, a return on which would be necessary," he told reporters.

"That sounds more like a loan than anything else."

The prime minister has previously said he hopes construction on the airport link can begin by 2020.