Damage to overhead electric wires means trains are unable to run between Slough and Paddington.
Train services at Paddington station are suspended, disrupting the journeys of mourners heading to London or Windsor for the Queen’s funeral.
Great Western Railway (GWR) said all lines between the west London station and Slough, Berkshire, are blocked due to damage to overhead electric wires.
The problem is affecting journeys for passengers travelling from Reading and Heathrow Airport.
Services run by GWR, Heathrow Express and the Elizabeth Line are disrupted.
The rail firm said Chiltern Railways, Transport for London (TfL) and Southern Railway are taking passengers via any reasonable route until further notice.
The lines between Reading and Newbury are also closed after a person was hit by a train.
This is causing GWR trains to be diverted, delaying journeys to the capital.
The issues come during one of the UK’s biggest transport operations as mourners descend on London and Windsor.