Dave James Phillips, a 39-year-old technology consultant from Britain, said he was getting off the last train in from London when he saw officers flooding the station.

"There were police immediately, and a chap with his hand on his gun," Mr Phillips told AP. "As we were walking down the platform, one came down and said, 'Rapide, rapide. Out, out.'"

Mr Phillips said police kept pouring into the station as passengers were hustled out and police buses and unmarked cars were "driving quite dramatically up the road."

Mr Phillips said he had since left the area. "Hopefully nothing happened," he said.

Benjamin, 29, had just got off a train from Lille at 11.15pm when police officers in "classic uniform asked us to leave the station fast".

"As we were going towards the metro, we crossed paths with a more heavily-armed police unit", equipped with bullet-proof shields, he told Le Parisien.

"When we passed by this police unit, people around us started to panic, shout and run towards the metro exits," he is cited as saying.

A Eurostar spokesman said the incident did not appear to have any relation to its trains and did not appear to affect its passengers. The operation began after the last Eurostar arrivals and departures late Monday.

France is under a state of emergency after a string of terror attacks in the last two years left more than 230 dead. The latest occurred on April 20 when an Islamist radical shot dead a policeman on the Champs-Elysées in Paris before being gunned down by other officers.