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.
More top news
Kate Haskell has the weather for the east of the region
Kate Haskell has the weather for the west of the region
Police said they are concerned for the welfare of 13-year-old Serena Alexander-Benson.