Southern Rail said trains are being delayed 'due to a number of incidents' between Gatwick Airport and Three Bridges.
"Delays have occurred because passengers have caused a disturbance on board a train which emergency services will attend," a spokesperson wrote on Twitter.
"There is also planned engineering work, meaning there are less platforms than normal available at Three Bridges and there was an operational incident.
"You may need to allow up to 15 minutes extra to complete your journey this evening."