Train delays of up to 10 minutes are being caused because of signalling faults in Ipswich.
Services are running at reduced speeds on some lines.
Greater Anglia spokesman said: “Network Rail engineers are working as fast as possible to fix the problem, which involves some of the signals at Ipswich station, affecting trains in the Norwich-bound direction only.
“An estimate for the resumption of normal services will be provided as soon as the problem has been fully assessed.”
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