Rail passengers across England are facing disruption after electric wires in London were damaged.
There will be no services in and out of London Euston until at least midday while repair work is carried out, Network Rail said.
More than 500m of wire in the Wembley area needs to be replaced after it was damaged on Friday, it added.
West Coast main line services between London Euston, Watford Junction, Birmingham and Manchester are affected.
Engineers were working "as quickly as possible", a Network Rail spokesman said.
He said the company was "unsure at this stage of the cause of the damage".
"We're asking everyone to check National Rail Enquiries before they travel so they have the most up-to-date information," he said.
London Euston station will remain open despite the line closures.
Passengers using Virgin, London Midland and London Overground services will be affected and delays are expected throughout the day.