Inner-city traffic will worsen, 744 trees will be lost and riverfront views blocked if the Andrews government does not immediately change key parts of the West Gate Tunnel's design, Melbourne City Council has warned.

The council has made a last-ditch bid to change the design of Transurban's new toll road in a report released one day after Premier Daniel Andrews announced that the $6.7 billion project was under construction, despite key planning approvals and legislation not having passed Parliament.

"Management remains very concerned about the project’s impacts on the City of Melbourne and its community," the report says.

An artist's impression of the proposed West Gate Tunnel as it crosses the Maribyrnong River. Credit:Victorian government

The new toll road will link the West Gate Freeway in Spotswood with CityLink in Docklands by tunnelling underneath Yarraville.