Trespassers on the railway line are causing delays to train services from Ipswich to Cambridge, Greater Anglia says.
The 1.20pm train from Ipswich to Cambridge train station has been terminated at Bury St St Edmunds, due to people on the tracks.
This means it will no longer call at Kennett, Newmarket and Cambridge.
The trespassers have also caused the 2.46pm Cambridge to Ipswich to be cancelled.
It is unclear if any other services will be cancelled while the incident is being dealt with.
British Transport Police have been approached for a comment.
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