Train services between East Anglia and the capital are delayed or cancelled after balloons became caught in overhead wires.
The balloons became caught in the electric wires at Witham in Essex earlier on Tuesday evening.
Services running through the station are being disrupted as a result.
A Network Rail response team is en route to deal with the incident.
In a statement, Greater Anglia said: "Due to balloons caught on the overhead wire trains in the Witham area are being disrupted.
"A Network Rail response team are aware and en route to Witham."
Disruption is expected until further notice.
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