All trains on the East Coast Main Line have been stopped because of a "huge number" of trespassers trying to see the iconic Flying Scotsman train on its journey from London to York.
The Flying Scotsman itself was also stopped as Network Rail warned people not to trespass on the railway to try and get a better view.
The train arrived at King's Cross station in London today for its inaugural journey after a decade-long £4.2 million refit.
We've had to stop all trains on the East Coast Main Line incl. #FlyingScotsman because of huge number of trespassers. Please, don't.
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Thousands of rail fans were expected to line the tracks and bridges along the route as the famous locomotive, built in 1923, travels up the line.
Network Rail said it had to stop all trains due to trespassers, warning that it was "hugely dangerous" to step onto the tracks. It has now restarted trains "at slow speed".
Lots of safe vantage points for pics of #FlyingScotsman - don't be tempted to trespass on the railway, hugely dangerous. Please, stay safe— Network Rail press (@networkrailPR) February 25, 2016
Trains now running at slow speed as trespassers clear the tracks - please, enjoy #FlyingScotsman safely and stay off the railway— Network Rail press (@networkrailPR) February 25, 2016
The train has been restored for 10 years and returned to its original 'British Rail green'.
Named after the train service between London and Edinburgh, The Flying Scotsman was the first to travel the journey at 100 miles per hour.
Once in York it will go on display at the National Railway Museum until 6 March before setting off on a tour around the country.
The museum's head curator Andrew McLean said that seeing the train "looking exactly as she should, in steam and alive again" would be a "really special moment for many people".