Cranbourne and Pakenham lines have been suspended on Tuesday morning due to vandalism, the Department of Transport reports.
Buses continue to replace trains between Oakleigh and Dandenong.
Gippsland V/Line services will terminate and originate at East Pakenham, with passengers asked to board the Metro replacement buses.
Metro Trains will continue to run between Flinders Street and Oakleigh, Dandenong and East Pakenham and Dandenong and Cranbourne, with delays to these services.
It is expected this suspension will continue into the late morning.
Passengers are asked to check station platform displays, listen for announcements, and to allow an extra 30 minutes travel time for their journey.
Services will resume as soon as repairs are complete.
Signals team is monitoring conditions in the area and will adjust traffic lights to assist with bus movements.
Real-time traffic conditions are available at traffic.transport.vic.gov.au. The latest public transport information and network status is available at ptv.vic.gov.au, and V/Line network status is available at vline.com.au
