A plastic bag is causing delays between St Albans City and West Hampstead Thameslink.
The bag has been caught in the overhead power lines and has caused one of the southbound lines to be shut and delays of up to ten minutes.
Trains which usually call at platform three at Radlett, Elstree & Borehamwood, Mill Hill Broadway, Hendon, Cricklewood, may now arrive and depart from platform one.
The disruption is expected to last until 5.30pm.
To follow this incident on Twitter, use #StAlbans
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