Trains travelling from London to Windsor, where Queen Elizabeth will be buried later on Monday, were severely disrupted by technical problems, straining the public transport system as tens of thousands travel around the capital.
Great Western Railway (GWR) said that all lines between Paddington and key connection point Reading, were blocked, advising passengers to take an alternative route to Windsor, the town that is home to the Windsor Castle royal residence.
In an update issued at 0930 GMT, GWR said the disruption was likely to continue for the rest of the day.
Later, the queen's coffin is due to be driven to Windsor, where she will be buried alongside her late husband Prince Philip in a small chapel in a private ceremony after the funeral. Large crowds are expected throughout the town.