Transport Minister Philippe Tabarot said that almost 500 trains were cancelled and the disruption affected around 600,000 people at the Gare du Nord, France’s busiest train station.

It wasn’t immediately clear how the bomb was made safe or disposed of.

“We’re delighted and relieved that all this has come to an end,” he said, adding that a major highway was immediately reopened after it was closed for several hours. Train services resumed from 6pm local time (4am Saturday AEDT).

Rail services were halted at Gare du Nord, upending commuters’ workdays and travellers’ weekend getaway plans, as bomb-disposal experts worked to make the 500kg explosive device safe.

Eurostar, the operator of sleek high-speed trains through the Channel Tunnel that joins England with the European continent, said it expects normal traffic between Paris and Brussels and between Paris and London on Saturday.

The company said it will run two extra trains, one leaving London to Paris in the morning, the other from Paris to London in the afternoon.

The cascade of transportation woes first hit morning rush-hour train services before also spreading to the road network, with Paris police closing the A1 highway that feeds into the north of the city, as well as sections of the capital’s always-busy ring road, as the bomb-disposal operation dragged on.

Eurostar announced the cancellation of all its services linking its Paris hub at Gare du Nord to the UK and Belgian capitals. Scores of commuter, regional and high-speed trains between Paris and towns and cities in northern France were also cancelled.

Travel plans thrown into disarray

Gabrielle Cotton, a tourist from the US state of Missouri, was trave=lling by train from Amsterdam in the Netherlands to Paris, but got no further than Brussels.

“I heard the girl next to me — her parents called her and said that there was a World War II bomb found in the train station,” she said.

“They told us we had to get off in Brussels.”

Retired Parisian Michel Garrot also found himself stranded with his wife in the Belgian capital.

“There’s no solution. We’re going to call the hotel and stay one more day. And change our train ticket,” he said.

At Eurostar’s hub in London, St. Pancras International station, passengers scrambled for alternatives. Fridays are invariably busy with thousands of weekend travellers. Paris-bound passengers were advised to try taking trains to Lille in northern France, or fly.

Bride-to-be Charlotte Liddell had a bachelorette party — her own — to get to in Paris and wanted to join friends already in the French capital.

“It’s the hen do without the hen!” she said.

“We’re very upset, but it’s so out of our control.”

Another traveller, Lee Bailey, said Eurostar offered him a free rebooking or a refund, and an apology, but no compensation.

“I’d like to go to a Michelin (starred) restaurant in Paris on their dime, but that’s not happening, apparently,” he told Sky News.

Eurostar said it “sincerely apologises for the disruption and understands the inconvenience this may cause.”

The bomb was dug up overnight

Workers laboring overnight on a bridge-replacement project spotted the 500kg bomb before dawn on Friday, after it was found by an earth-moving machine at a depth of about 2 metres, between train tracks to the north of the Gare du Nord station, in the Seine-Saint Denis region that borders northern Paris, the national rail operator SNCF said.

Bomb disposal services arrived within the hour and set up a 200-metre security perimeter, later extended to 500 metres. Tabarot said that 300 police officers worked to secure the area.

“This was no small operation,” Tabarot said.

When morning rush-hour travellers later started arriving at Gare du Nord to catch trains, they were greeted by bright-red signs warning of disruptions, lines of passengers seeking information and ticket-exchanges, and barriers blocking access to the Eurostar terminal.

The Gare du Nord habitually hosts 700,000 travellers per day, making it the busiest rail hub in both France and Europe, the SNCF says.

As well as towns and cities across northern France and the Paris suburbs, the station also serves Paris’ main airport and international destinations, including London, Brussels and cities in the Netherlands.

Deadly legacies of World War I and II

Bombs left over from the battles fought in France and its skies in both world wars are regularly unearthed, even more than a century later, although it’s rare that they cause such widespread disruption in people-packed Paris.

In World War II, Allied forces’ bombing raids flattened towns and cities in the Normandy region northwest of Paris but didn’t wreak destruction on the same scale on the French capital.

Still, factories, train lines and other targets in and around Paris were bombed repeatedly, killing more than 3600 people and wounding thousands more, according to city archives.

The Interior Ministry says that since World War II’s end in 1945, disposal teams have defused 700,000 air-dropped bombs and made safe nearly 50 million mines, shells and other explosive devices.