Drilling work has begun in Melbourne's CBD as part of the multi-billion-dollar Melbourne Metro rail project to add five new train stations and upgrade the City Loop.

The geotechnical work will examine ground conditions and soil quality to determine the exact alignment and depth of the tunnel under Swanston Street.

Melbourne's CBD is facing years of major disruption once construction of the new $11 billion tunnel gets underway, including the closure of Swanston Street and the re-routing of trams.

Swanston Street is the city's busiest tram corridor.

Public Transport Minister Jacinta Allan said every effort would be made to minimise the impacts.

"That's why the geotechnical work is important so they can really pinpoint where different services are underground and what the alignment will be like underground to try and limit the disruption," she said.

"Any big project of this size will cause disruption."

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Ms Allan said major tram maintenance work scheduled for Swanston Street this weekend will give Melburnians a taste of the disruption likely to be caused by the project.

"The vital maintenance work Yarra Trans will be undertaking along Swanston Street will give people a bit of a sense of what disruption will be like," she said.

"It's been identified that maintenance work is needed now along Swanston Street."

It is expected the Melbourne Metro project will allow an extra 200,000 passengers to travel during peak hour.

Melbourne's Lord Mayor Robert Doyle said the project was vital as the city continued to grow.

"This is a city-changing project and it will set our city up for the next 50 to 100 years," Cr Doyle said.

"There will be disruptions, we understand that.

"We will work with our trades, with residents, with everyone affected along the route."

The Government has begun consultations with CBD residents and traders who will be affected by the construction, which is due to begin in 2018.