First trains tested in Melbourne's $12.6b Metro Tunnel

Melbourne's long-awaited $12.6 billion Metro Tunnel has moved a step closer to opening, with the first trains testing out the infrastructure.

Trains ran in each of twin nine-kilometre tunnels from South Yarra to Anzac Station overnight, marking the start of project testing.

The trains travelled at between 5km/h and 25km/h for the test.

Premier Daniel Andrews toured the new Anzac Station on Tuesday and denied the project was over-budget.

"It's been delivered against the budget that's been allocated," he told reporters.

The Metro Tunnel is expected to open in 2025.