Around 1,800 people were evacuated from the area around Paris's Gare du Nord station at 6h00 on Sunday when the demining operation began.
Most have been waiting in local gymnasiums, a few dozen in the nearby Town Hall.
The unexploded bomb was discovered on 4 February this year during engineering work in the area north of Gare du Nord, served by Eurostar.
Local media reported that previous attempts to neutralise the bomb had failed. But Paris Mayor Anne Hidalgo tweeted in the early hours that the operation was being undertaken in the best possible conditions.
Nous sommes à présent à la @mairie18paris. Nous accueillons ici aussi plusieurs dizaines d'habitants. L'occasion de remercier la @CroixRougeParis et la @PCParisSeine : elles sont sur tous les fronts et elles sont une fois de plus mobilisées ce matin. 👏👏 pic.twitter.com/K4OYkr0kUZAnne Hidalgo (@Anne_Hidalgo) 17 février 2019
There's been major disruption to transport in and out of Gare du Nord however.
Five Eurostar services between the French capital and London were cancelled on Sunday.
And normal services for local trains to and from the station will not resume until 15h Paris time.
Eurostar has offered free exchanges or refunds for passengers booked to travel on Friday, Saturday or Sunday.