Public transport users are being warned to prepare for three days of headaches as a tram strike and rail works hit the network.

Key points: All Melbourne tram services will stop between 10:00am and 2:00pm today

All Melbourne tram services will stop between 10:00am and 2:00pm today People are being advised to avoid non-essential travel

People are being advised to avoid non-essential travel The tram strike will be followed by major rail disruptions from tonight until Sunday night

Melbourne's trams will be replaced by buses today as drivers walk off the job over a pay dispute.

Then from tonight, trains on nine lines will be replaced by buses until the last service on Sunday night, for maintenance and power upgrades.

This will lead into a three-year closure of parts of Flinders Street to make way for Metro Tunnel works.

Strike to bring trams to a stop

Yarra Trams drivers and customer service staff will strike for four hours, bringing the network to a halt between 10:00am and 2:00pm.

While Yarra Trams has said the four-hour stoppage should not affect the peak hour commute, Public Transport Victoria (PTV) has warned passengers to prepare for disruptions as early as 9:00am and as late as 3:00pm because trams will have to return to depots during the strike.

Buses will replace trams, but PTV has warned they will run every 20-30 minutes and will not service the entire network.

Significant delays are expected on replacement buses and there will be bigger crowds on trains

The Victorian Government says it is working hard to minimise disruption. ( ABC News: Nicole Asher )

The Rail, Tram and Bus Union (RTBU) is fighting for a 6 per cent annual pay rise and an end to Yarra Trams' plans to scrap a 4 per cent cap on part-time jobs.

RTBU state secretary Luba Grigorovitch said the union had done its best to minimise the strike's impact on commuters.

"RTBU members deserve a fair and just [Enterprise Bargaining Agreement], we can't rule out further protected industrial action if Yarra Trams continues down this path."

The Transport Department's head of transport services, Jeroen Weimar, apologised in advance to passengers.

"It's disappointing that this dispute will inconvenience the thousands of Victorians who rely on Melbourne's trams to get where they need to go each day," Mr Weimar said.

"We encourage all parties to continue negotiating to reach a satisfactory agreement in the interest of passengers."

City Loop to close, buses to replace trains

Bus services will replace trains on a number of lines. ( ABC News: Danielle Bonica )

Today's tram strike comes ahead of a weekend of major disruptions across the train network from 8:20pm today until the last train on Sunday.

The City Loop will be closed to all trains, and trains will replace buses on sections of nine metropolitan lines, as well as the Geelong, Warrnambool and Gippsland lines, while power upgrades and maintenance works are carried out.

Buses will replace trains between Parliament and Caulfield stations on the Cranbourne, Pakenham and Frankston lines, and between Parliament and Elsternwick on the Sandringham line.

On the Werribee and Williamstown lines, bus replacements will run between Flagstaff, Newport and Williamstown.

Trains will be replaced by buses from Flagstaff to Sunshine on the Sunbury line, to Essendon on the Craigieburn line and to the end of the Upfield line.

Parts of Flinders Street to close for Metro Tunnel works

The disruptions will not stop on Sunday night — from Monday, parts of Flinders Street will be closed to cars for up to three years.

The closure of eastbound lanes, between Elizabeth and Swanston streets, will pave the way for underground work connecting Flinders Street Station and the new Town Hall Station.

Transport Infrastructure Minister Jacinta Allen said the series of works had been widely advertised so passengers could plan ahead.