No trains are running between Colchester and Ipswich following a signal failure.
Greater Anglia has reported mainline services are being disrupted due to a loss of signalling between Ipswich and Stowmarket.
A spokesman said: "Train services between London Liverpool Street and Ipswich are suspended between Colchester and Ipswich.
"A replacement bus service is in the process of being arranged, but is not yet in place."
Passengers have reported being told to get off trains at Colchester station.