Train at WGC station (Image: Archant)
A broken down train is causing delays of about 20 minutes on southbound services.
The train is currently blocking the track at Brookmans Park Station, affecting trains running through Knebworth, Stevenage and Hitchin.
A spokesman for Great Northern said the problems were due to a door fault.
Great Northern tweeted: “Ongoing delays on the SOUTHBOUND line of up to 20mins following a broken down at Brookmans Park.”
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