All trains out of Lowestoft are being cancelled, delayed or revised due to a signalling fault at Oulton Broad North.
Trains to and from Norwich and Ipswich are unable to run to Lowestoft, with all services diverted to Great Yarmouth.
Greater Anglia said on Twitter: 'Due to a fault with the signalling system between Oulton Broad North and Lowestoft all lines are blocked.
'As a result train services between Norwich and Lowestoft will be diverted to Great Yarmouth. A rail replacement bus will operate between Great Yarmouth and Lowestoft.'
They added: 'Ipswich to Lowestoft services will terminate and start from Oulton Broad South. Greater Anglia tickets will be accepted on local buses X2 and X22 between Beccles and Lowestoft.'
There is also a replacement bus service to Oulton Broad South for passengers travelling to Ipswich.
National Rail also said on Twitter the disruption was expected to last until at least 6pm.
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