Rail services between Chichester and Portsmouth are subject to delays due to a problem with a level crossing barrier and a trespassing incident.
Southern Railway said there has been a problem with a level crossing at Havant as well as a trespass incident in Fareham.
Services between Havant and Fareham may be cancelled, delayed by up to 30 minutes or revised as a result.
Disruption is expected until 7pm, Southern added.
Southern said tickets can be used for travel with South Western Railway services between Havant, Portsmouth Harbour and London Waterloo, and on Stagecoach Route 700 bus services between Chichester and Portsmouth.
Southern services may terminate short of the original destination at either of the following: Barnham, Chichester, Havant or Fratton.
In a statement, Southern said: “Earlier today it was reported that there was an issue with a level crossing barrier at Havant. It is believed that the barrier was damaged by wind. Network Rail engineers are on site and are working to repair the issue. Trains are able to run through the area, however are being ‘talked’ past signals in the area for safety reasons. This means that it will take longer for trains to run through, and therefore will become delayed.
“Unfortunately Southampton services have been further delayed in the Fareham area due to a group of trespassers who have then proceeded to throw obstacles onto the track, and as a result trains are currently at a stand in the area. Network Rail operatives are working to get the track clear in order to allow services to continue to run through.”