A points failure at St Pancras International just before noon on Thursday (November 25) has stranded one train in a platform and left others struggling to enter and leave the platform.
The train operator, which runs InterCity and Connect services through Northamptonshire, has warned of delays of up to 30 minutes.
A spokesman said: "Network Rail engineers are now testing the points and at present we expect to be able to resume our advertised timetable by 2pm.
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"Trains are running through the area in both directions but may be delayed by 30 minutes between Luton and London.
"We are sorry for the delay to your journey today but if your overall journey is by over 15 minutes you may be entitled to claim compensation via our website."