Industrial action is affecting services on Southern trains, with RMT Union members beginning strike action.
This walkout is expected to last five days, with Southern warning all trains will be hit until end of service on Friday.
No Southern trains will run on routes between Clapham Junction-Milton Keynes Central; Dorking-Horsham; Oxted-Uckfield; and others.
No trains will operate to or from Earlswood, Salfords and Faygate.
It is believed to be the longest rail strike since 1968, with Southern-parent Govia Thameslink involved in a dispute with the RMT over plans for drivers to operate doors on new trains using CCTV.
RMT members this fear will lead to redundancies for train guards, something the train operator denies.
Southern said it hoped to operate around two thirds of its services.
RMT general secretary Mick Cash said: “I can report that the strike action this morning is rock solid across the Southern Rail network as we fight to put rail safety before the profits of the failed Govia Thameslink operation.
“This action has been forced on us by the arrogance and inaction of Govia Thameslink and the government who have made it clear that they have no interest in resolving this dispute or in tackling the daily chaos on Southern.
“We offered to suspend the action on Friday if they matched the offer we secured on Scotrail.
“They kicked that back in our faces.”
Passengers have been urged to check National Rail for the latest train timetables.