A plan to build Australia's biggest port at Hastings, south-east of Melbourne, relies on also building the state's biggest public transport project, the Melbourne Metro rail tunnel, putting the Napthine government at odds with its federal allies.

The federal Coalition has ruled out funding passenger rail projects, including Melbourne Metro, but on Wednesday committed $300 million towards building an inland freight rail line between Melbourne and Brisbane.

Illustration: Ron Tandberg.

The Rudd government on Tuesday committed the same amount to early work on the line, which would ultimately cost $5 billion to build.

Nationals leader and shadow transport minister Warren Truss said the inland rail line ''has the potential to take up to a million semi-trailers a year off the road by transferring freight that otherwise would have moved by road onto the rail network''.