A report in the Herald Sun noted a decision was "imminent" from the state government on whether to build the tunnel, between Southern Cross and Sunshine, or to use existing tracks and the Melbourne Metro Tunnel, which is currently under construction.

The report states the tunnel plan, which could cost up to $20 billion, is supported by a private consortium that has offered to pay $7 billion for construction in exchange for the right to charge access fees for other trains using the tunnel.

WHERE TO START: A non-trainspotter's guide to the Ballarat rail debate

The state and federal governments would then pay the rest of the money.

Experts have commented building the tunnel would create space for additional regional trains between airport-only trains, bringing fast rail to Ballarat and Geelong a step closer.

The state government has consistently said it is reviewing its options and no decisions have been made yet.

The federal government has allocated billions of dollars for an airport rail link and fast regional rail - during the 2019 election, the Coalition promised $2 billion for fast rail to Geelong.

In a statement, Committee for Ballarat chief executive Michael Poulton said he had doubts about the $20 billion cost estimate, saying it was "well over the initial projections" of $8 to 13 billion.

"We have confidence in the market-led proposal led by IFM (the consortium), as they are the major investors in the project and have committed $7 billion. It is in their interests to cost this accurately," he said.

"The tunnel is the only option currently in the table that enables the next generation of fast, high frequency regional rail to the growing cities of Ballarat, Bendigo and Geelong, whilst at the same time, ensuring the western suburbs massive growth needs are catered for. The state government's proposed Melbourne Metro tunnel (solution) does not solve the demands for growth of regional rail."

However, he said rail infrastructure works could be a way of stimulating the post-pandemic economy.

"We are encouraged by Minister Pakula's public comments here in Ballarat at the Commerce Ballarat Biz Breakfast that the state will look to major infrastructure as a way out of COVID-19 and will look to partner with private investors to secure new infrastructure projects," he said.

The state government committed $100 million to the Western Rail Plan over four years, which will determine the next steps to improve rail infrastructure.

Independent rail advocate Nick Beale was optimistic - he said the planned quadruplication between Melton and Sunshine, which would allow regional trains to bypass suburban stops like Rockbank, should be prioritised ahead of other proposals, like the ambitious Suburban Rail Loop, which would create a rail link across Melbourne's outer suburbs.

"If the consortium offer is rejected, this would be a pity - however, we don't need the $20 billion overall cost of the tunnel to go all to the taxpayer," he said.

"As long as the connection between Southern Cross and the airport is complete, Ballarat would remain advantaged by the airport link - the quadruplication will assist in quicker services, and more services, into Southern Cross.

"I do think that the spaghetti of Southern Cross Station does need a better solution."

Have you signed up to The Courier's variety of news emails? You can register below and make sure you are up to date with everything that's happening in Ballarat.