Early morning train services between Inverness and Aberdeen have been cancelled.
A safety inspection is underway between Elgin and Keith after reports of a possible defect on the tracks.
Disruption is expected to last until at least 09:30 this morning.
A ScotRail spokesman said: “Train services between Aberdeen and Inverness will be cancelled, delayed or revised.
“We have reports of a possible track defect between Elgin and Keith and therefore cannot run trains through the area until our staff have carried out an inspection.
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“Staff have given an estimated time of 08:00 to be on site and we will update as soon as we have more information.
“Currently, we have not requested rail replacement transport. We will monitor this situation as the incident develops.”
The first service to be affected was the 05:49 Inverness to Aberdeen due in at 08:05, which terminated in Elgin.
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The 06:14 Aberdeen to Inverness, due 08:26, was terminated at Huntly.
An additional 07:12 Huntly to Inverness service scheduled has now been cancelled.
But an additional train service has been laid on to operate from 07:43 from Elgin to Inverness, due into the city at 08:26.
The 08:26 Aberdeen to Inverness service has also been cancelled.
All passengers are advised to check ScotRail’s and National Rail’s websites for updates, with changes of schedule and further cancellations possible throughout the morning.