Updated (8.40pm): Some services resume between Ipswich and Stowmarket following signal failure
Engineers are trying to fix a problem on the railway line between Ipswich and Stowmarket which has led to a complete loss of signalling.
All routes are affected on the stretch of track leading to potential disruption on services between Ipswich and Colchester, Diss, and Stowmarket.
There is also the possiblity of knock-on delays for other services between London Liverpool Street and Norwich, and services from Ipswich to Ely, Peterborough and Cambridge.
Some services have already been cancelled.
Engineers from Network Rail were called to the fault at around 4.45pm.
Rail operator Abellio Greater Anglia is currently trying to arrange bus replacement services on all routes.
Tickets are being accepted on other rail routes between London, Ely and Norwich.
Some London to Norwich services are now able to travel through the affected area, but at heavily reduced speeds.
However the knock-on effect of the earlier disruption means services are still subject to alteration or cancellation.
Trains from Ipswich to Cambridge and Peterborough remain cancelled for the rest of today, with a bus replacement service in operation.
The disruption is expected to last until at least midnight tonight.
The rail operator has said an hourly service will run from London to Ipswich.
Passengers travelling from London to Norwich or Stowmarket are advised to travel via Cambridge.
A bus replacement service will run between Ipswich, Stowmarket and Diss, and a shuttle train service will run from Diss to Norwich.
An Abellio Greater Anglia spokesman apologised for the inconvenience caused and reassured passengers that engineers from Network Rail were on site and working to resolve the problem as quickly as possible.