Services are being disrupted between London Waterloo and Andover, Basingstoke, Bournemouth, Portsmouth Harbour and Southampton Central today (November 9).
National Rail says that police are dealing with an incident near the railway at Basingstoke station.
All lines were closed for over 30 minutes, disrupting London-bound routes.
Although no further information about the police incident has been shared, staff have aided response teams by powering the tracks off.
South Western Railway says that all lines have since reopened, but trains may still be cancelled for up to 50 minutes.
Disruption is expected until 9pm.
