Footage on social media shows travellers crammed on the platforms at Gare du Nord station as passengers claimed an evacuation was ordered because of a "bomb threat".
It was also reported a "loud controlled explosion" was heard shortly after people were cleared from the station.
Witnesses said the security scare had sparked panic in the station as "massive" queues formed on the concourse and other trains were delayed.
Several people alleged the ornament was brought on a train heading towards London.
Martin Adams tweeted: Evacuated from Gare du Nord in Paris-then heard v. loud controlled explosion after tourist tried to bring WWII bomb back to London..!
Eurostar passengers were cleared from Gare du Nord station in Paris (stock image)
Another social media user added: "Eurostar Gare du Nord evacuated: when a moron tries to carry a fragment of WWII bomb in his luggage from Paris to London."
Eurostar confirmed services had been halted after "somebody tried to take through a military relic" while other passengers were told a "suspect package" was under investigation.
Mirror Online have approached Eurostar for comment.
We'll be bringing you the very latest updates, pictures and video on this breaking news story.
For the latest news and breaking news visit Mirror.co.uk/news .
Get all the big headlines, pictures, analysis, opinion and video on the stories that matter to you.
Follow us on Twitter @DailyMirror - the official Daily Mirror & Mirror Online Twitter account - real news in real time.
We're also on Facebook/dailymirror - your must-see news, features, videos and pictures throughout the day from the Daily Mirror, Sunday Mirror and Mirror Online.