Southern Rail said there was a vulnerable person on the railway between Havant and Portsmouth Harbour. The person is safe and trains are going to be able to run through the area at normal speed again very shortly.
A spokesman added: “We still recommend checking your journey before travelling between Havant and Portsmouth this morning.”
Southern Rail and Thameslink also warned this weekend trains to and from Brighton will be busier than usual.
A spokesman said: “Please allow extra time if travelling.
“Plan your journey. Wear a face covering in crowded spaces if you are not exempt. Be prepared to queue.