Rush-hour train journeys between Glasgow and Aberdeen have been disrupted due to safety checks on the line.
It is understood the line south of Stonehaven was vandalised overnight, resulting in delays of up to 30 minutes for people travelling towards Aberdeen from Dundee on Monday morning.
Journeys between Edinburgh and Aberdeen have also been affected.
Passengers travelling to the city are being taken by bus from Dundee and Montrose and trains are currently starting and being terminated at Laurencekirk station.
Network Rail confirmed the delay to services on its website, but did not give an estimate for when normal services will resume.