The Flying Scotsman made a triumphant return to the tracks when it set off on its inaugural run from London to York on Thursday after a £4.2m 10-year refit.
One of the world's most famous steam trains, the iconic locomotive was watched by crowds as it set off from King's Cross station.
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Thousands of trainspotters are expected to head to the tracks and bridges up the East Coast Main Line to catch sight of the Flying Scotsman as it makes the non-stop journey.
There are 297 VIPs on board for the five-hour trip, including former MP Michael Portillo, who is filming BBC documentary Great British Railway Journeys.
Speaking to ITV News, he said: "It's absolutely wonderful that it's able to run today from London to York.
"We've got a very excited bunch of passengers. We've got a whole lot of history."
Meanwhile, enthusiasts are reportedly being warned to stay off the tracks after trespassers brought the locomotive to a "shuddering stop".
Network Rail: The Flying Scotsman was stopped in Cambridgeshire due to enthusiasts on the tracks..it's now underway again at a slower speed
— BBC Radio Sheffield (@BBCSheffield) February 25, 2016
Network Rail said it "had to stop all trains on the East Coast Main Line incl. #FlyingScotsman because of huge number of trespassers."
It added: "We're reminding people: Keep off the tracks. Stay safe. There are live trains running. #StaySafe #FlyingScotsman"
Virgin Trains East Coast tweeted about delays to its services and said: "Due to eager #FlyingScotsman photographers on the track near Peterborough, delays of 15 mins are expected. Don't be silly!"
The Flying Scotsman was bought by the National Railway Museum in York for £2.3 million in 2004 before its restoration began.
Jim Lowe, head of operations at the museum, told Sky News: "Along with all our generous supporters for this complex project to bring a 1920s-built cultural icon back to life, we have all been looking forward to this historic day when Flying Scotsman steams again."
The Flying Scotsman will tour the country from 6 March.