In a press conference on Tuesday morning Premier Daniel Andrews announced the closure of nine train lines across the city and state beginning in April.

Andrews described the works as “one of the most significant disruptions to our public transport that we’ve ever seen”.

Busses will replace trains on the Cranbourne, Pakenham, Frankston, Sandringham, Mernda, Gippsland and Geelong/Warnambool lines from April 1 to 23. A government spokesperson confirmed to Broadsheet the works will affect 1.5 million people.

Travellers affected by the closures are being advised to allow for up to an hour of extra travel time.

The closures mark the beginning of construction of the South Yarra entrance to the $11 billion Metro Tunnel, but works also include projects across the state such as the removal of level crossings and further rail upgrades.

The Sandringham, Frankston, Cranbourne/Pakenham and Dandenong lines all converge at South Yarra station. The lines need to be separated and the Dandenong line directed underground so that they can enter the Metro Tunnel. Freight and V Line services will continue to go through South Yarra station after the closure.

“We want to apologise in advance … for the inconvenience that it will cause the travelling public, but it is essential that we close these lines, that we have interrupted services,” said Andrews.

Following a series of major disruptions, travel to Gippsland will be free during the period and express bus services will be scheduled.

Richmond Station will also close as part of the final phase of the 18-month upgrade to the Cranbourne/Pakenham line. All lines through the station will be closed over the three-week construction period, except for the Alamein, Belgrave and Lilydale lines. There will also be disruption to the Glen Waverley line.

During the Richmond Station closure works will be completed between South Yarra and Flinders Street Station on power and signalling upgrades to make way for new high-capacity trains. During the AFL season, the Free Tram Zone will be extended to accommodate for the closure of Richmond Station.

“There will be significant and unprecedented disruption during April. It can’t be avoided,” said Andrews. “If we don’t have some construction-related disruption today, if we don’t build these projects today, we will have nothing but disruption and chaos into the future.”

For updates on the works, line closures and replacement services go to to big bigbuild.vic.gov.au