The work is being carried out across the area, and some people may need to use a bus replacement service to complete their journey.
On Southern Rail, buses will replace trains between Havant and Portsmouth Harbour.
On South West Trains, buses will replace trains between Havant and Portsmouth Harbour, and Cosham and Portsmouth Harbour. A special service will operate between Cosham and Havant, calling at Bedhampton.
On Great Western Railway, trains will not run between Fareham and Fratton, and Fareham and Portsmouth Harbour. Buses will replace trains between these stations.
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Services are also altered between Woking and London Waterloo.
The work is due to be completed at approximately 3.45pm.
Visit nationalrail.co.uk to check your train times.