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 morning's weather for the west of the region
Wednesday morning's weather for the east of the region
A new report into the ever- worsening traffic congestion in Oxfordshire has concluded that the county is in danger of coming to a halt.