All trains between Hounslow and Syon Lane were blocked on Thursday afternoon while the police dealt with an incident near the railway.
Services could not stop at all stations between Barnes Bridge while the emergency services responded to the incident.
Lines have since reopened but National Rail has warned that trains may still be delayed by up to 60 minutes or cancelled. Disruption is expected until 7pm.
Rail passengers are facing a third consecutive day of strike action on Thursday.
Members of Aslef at LNER, TransPennine Express and Northern Trains are walking out for the day following similar action over the past two days at other operators.
LNER will run more than 40 services between London, Edinburgh and West Yorkshire, equivalent to around a quarter of its usual timetable.
Aslef members at 16 train operators are continuing with a week-long ban on overtime which will also cause disruption to services until the weekend.
The Gatwick Express is also not running due to the strike action.
