South West Trains is advising passengers to travel only if absolutely necessary as services may also be cancelled or amended at short notice.
Jake Kelly, customer service director for the South West Trains-Network Rail Alliance, said: "In common with other transport operators in the area, we are experiencing severe disruption on our network as a result of freezing weather conditions this morning.
"Icy conditions are making it extremely difficult to operate our services and I am sorry to say that is resulting in lengthy delays for our customers.
"We would like to apologise to passengers for the inconvenience this will undoubtedly cause them. We have extra staff at our key stations to assist customers and provide information and we are keeping passengers on board our services updated as best we can."
He added that engineers are "working hard" to clear ice from the track but that today will be a "difficult day".
Passengers planning to travel are advised to visit www.southwesttrains.co.uk or call National Rail Enquiries for the latest service updates before they travel.
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