Train services from Horsham station are disrupted due to earlier emergency engineering works between Gatwick Airport and Horley.
Passengers journey times will be extended by up to 35 minutes with many services being cancelled or diverted at short notice.
It has also affecting First Capital Connect and First Great Western services.
A statement on Southern Rail’s website reads: “Southern and First Capital Connect tickets will be accepted on both operators services. Southern tickets will be valid on SWT services.
“METROBUS are accepting Southern Tickets Three Bridges to Redhill on Route 100. London Buses TFL are accepting Southern tickets Redhill to Purley- East Croydon on Route 405.
“For individual train information, please visit the National Rail Enquiries website, or call 08457 48 49 50.”