Train services between Paddington station and Heathrow Airport terminals are disrupted on Wednesday evening after a safety inspection.
Elizabeth line and Heathrow Express services are affected, with cancellations and delays expected until 9pm.
Earlier, Chelsea Bridge was shut to traffic after a serious collision involving a skip lorry and a cyclist.
The incident happened shortly after 8am on Wednesday on the north side of the bridge, near the Chelsea Embankment, leaving the cyclist badly injured.
The bridge was reopened at around 2.30pm on Wednesday.
The Metropolitan Police said no arrests have been made.
