South West Trains said that all services had been brought to a halt by the incident.
The company say they were briefly stopped and were now normal.
Thousands of passengers would have been on trains on that section of line at the height of the rush hour.
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Wednesday afternoon's weather for the west of the region
Wednesday afternoon's weather for the east of the region
A man's been treated in hospital after being hit by a police car responding to an emergency call in Brighton. It happened on Kings Road.