A police incident blocked trains between Fareham and Swanwick on Friday night.
At 9.54pm, Southern Rail tweeted to say that all lines were blocked between the two stations while police were 'dealing with an incident' that had 'recently happened'.
It was affecting services to and from Southampton Central station.
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At 10.05pm, the rail operator updated to say that 'power to the line was switched off for a short while due to a trespasser on the line'.
"The power has now been restored and we will be getting services back on the move shortly," Southern Rail said - although it warned passengers would face delays of up to 20 minutes.
At 10.59pm, Southern Rail said the disruption from the trespasser had ended.
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