London Fire Brigade (LFB) sent four fire engines and a further rescue unit to the scene at Marylebone station.
Twenty-five firefighters from Paddington, Soho, Kensington and Euston fire stations attended the incident in central London around 9pm on Friday.
The fire service initially said up to 700 people had been evacuated but later confirmed the number was 500.
LFB station manager Paul Hobbs said: "The fire was affecting one of the train`s carriages but crews worked quickly to put it out. Around 500 people have been evacuated from the station."
Shortly after 11pm National Rail said some services had begun to run again between Marylebone, which serves towns and cities in the northern Home Counties and West Midlands, and Banbury, Aylesbury and High Wycombe.
Chiltern Railways said on Twitter: "Thankfully no-one was hurt."
Disruption is expected until 1am and passengers are advised to visit the National Rail website to find alternative travel options.
LFB said the fire had damaged part of one of the train`s six carriages and an air conditioning unit underneath. The cause of the fire is under investigation.
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