High Wycombe – police were called to an emergency incident at the station
Eywitnesses said a train was evacuated as it waited at a platform following reports of a "man acting suspiciously" at the rear of a train.
Armed police told passengers to move "as far away as possible" as they surrounded the scene.
The station was evacuated as armed police swooped with services suspended for a short time during rush hour.
Both lines through High Wycombe are currently blocked due to the emergency services dealing with an incident
A National Rail spokesman said: "Due to the police dealing with an incident near the railway at High Wycombe, there are delays of up to 60 minutes to journeys between West Ruislip and Princes Risborough. This is expected to continue until 17.00."
Rail operator Chiltern Railways said: "Both lines through High Wycombe are currently blocked due to the emergency services dealing with an incident."
Police stood down shortly before 5pm following the hour-long operation.
Passengers were evacuated as armed police surrounded the station
British Transport Police said officers were called to support Thames Valley Police with the incident which was "not suspicious".
Thames Valley Police said the station in High Wycombe reopened shortly before 5pm after there had been reports of a "suspicious incident", saying that no offences had been committed.
Security is heightened in Britain following a suicide bomb in Manchester last week which killed 22 people.
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In the aftermath of the attack, British police put armed officers on trains outside of London for the first time.
Police cordoned off High Wycombe station
Britain's terror threat level currently stands at "severe" which means an attack is highly likely.