French officials have rejected suggestions they could resort to a "go-slow" policy at the port of Calais if there is no Brexit deal, reports the BBC.
The UK's Brexit secretary Dominic Raab warned on Thursday of major disruption in a "worse case scenario", which might force firms to use other ports.
But Xavier Bertrand, president of the Hauts-de-France region, said ensuring "fluidity" of trade was essential.
Another official said closing Calais would be an "economic suicide mission".
There has been widespread concern about the impact of longer border checks at Calais if the UK leaves the EU on 29 March 2019 without a deal.
Transport secretary Chris Grayling met the mayor of Calais, Natacha Bouchart, on Thursday to discuss French and British preparations for such an eventuality amid claims that businesses may be forced to use Dutch and Belgian ports instead to transport goods.