There is disruption on South West Trains services this morning between Guildford and London Waterloo due to a signalling problem between Egham and Surbiton.
Engineers are on their way to resolve the problem that means that London-bound services are unable to pass through the area.
It is not known when the problems will be resolved.
South West Trains are warning about cancellations and delays for services between Twickenham and Clapham Junction, between Feltham and Clapham Junction and between Twickenham and Hounslow due to over running engineering works between Barnes and Clapham Junction.
Waterloo to Reading services will run to Clapham Junction and be diverted via Kingston to Twickenham, with other services subject to diversions and alteration.
Tickets are being accepted on First Great Western, London buses, Underground and Overground.
The disruption expected to last until 07:00.
As thousands head off for the Easter weekend, commuters who travel through Reading are being warned of disruption as the station is closed due to £900m upgrade.
There are no direct services from Swindon, Oxford and Newbury to London. Trains from Bournemouth and Southampton to the north will also be affected. Here's our Transport Correspondent Mike Pearse.
First Great Western Managing Director Mark Hopwood explains in detail the changes to services and why the work is needed. He spoke to our Transport Correspondent Mike Pearse.
We have been treating the third rail in the south of England with anti-icing solution and trains were running around the network overnight to keep the rails clear of ice as much as possible.
Additional people were used on the ground to respond to incidents and carry out regular inspections of the infrastructure.
We will continue to work closely with train operators throughout today to deliver the best possible level of service and apologise for any disruption caused to passengers.
For the latest information, passengers should check with National Rail Enquiries or their train operator before travelling.
Services on parts of our network are being disrupted this morning as a result of adverse weather conditions which have also affected other train operators.
Cold weather conditions have caused a build-up of ice on the conductor rail which is used to power our trains.
When ice forms on the conductor rail it affects the power supply to trains and services are prevented from running normally.
As a result there are delays to services across some parts of our network. Services between Havant and Guildford are currently subject to delays of up to 60 minutes.
Trains between Waterloo and Reading are currently delayed by up to 30 minutes. Trains operating between Ascot and Guildford may be delayed by up to 40 minutes while services between Farnham and Alton are suspended.
We would like to apologise to customers for the delays to their journeys this morning.