Explosions in central London today hit travellers into and out of the capital.
Train passengers on the West Coast Main Line were being told not to travel to London following the blasts.
A Network Rail spokesman said southbound services into the capital were terminating at Watford with no onward bus transfers.
“Some trains are being cancelled and others are getting as far as Watford. The message we are trying to get across to passengers is don’t travel if you don’t have to,” he said.
Northbound services from Watford to Coventry, Birmingham and stations towards Manchester, Liverpool and Glasgow were running as normal, he added.
Chiltern Railways services into and out of London Marylebone through the Cotswolds to Birmingham Moor Street were also suspended, the company said in a statement.
“It is not clear when services will resume, but in the meantime, people are being advised by the police to avoid all travel to the capital,” they added.
The London to Paris and Brussels Channel Tunnel high-speed train company Eurostar was continuing services into Waterloo station in the capital.
A spokesman for the Airport Express Alliance which operates the Heathrow Express, Gatwick Express and Stansted Express train services said: “They are operating on injured people on the concourse at Liverpool Street station.”
He went on: “The Stansted Express is not operating as far as Liverpool Street and the Heathrow Express has suspended services. The Gatwick Express (which runs out of London’s Victoria station) is working normally.”
Airlines at Heathrow airport were operating normally, but it was expected that the events in central London could lead to some flight disruption.
A British Airways’ spokeswoman said: “With the Underground suspended, passengers and staff will face difficulty getting to the airport and our flights may well be delayed.”