Commuters and visitors arriving at York Railway Station on Thursday morning were met by armed police.
Firearms officers have begun patrolling the station in light of the raised state of alert across the country.
North Yorkshire Police said the move was designed to ensure the greater security of the county.
Despite their high-profile presence, a police spokesman said the force had not received any direct threat to the station or anywhere else in the county.
York is one of the main stations on the east coast mainline, which operates trains between Scotland, the north east, Yorkshire and London.
A police spokesman said on Thursday: "In view of a raised state of alert the force earlier this morning has begun patrols with armed North Yorkshire Police officers at York railway station.
"This situation will continue throughout the day."