Denis Robin, the state administrator in the region, said British authorities were willing to consider the cases one-by-one, such as if they can show they have kin already in Britain. In the meantime, France will consider temporary emergency lodging for them if they make formal requests for asylum.
"The contact has been made," he said. "In any case, the promises made will be kept."
But Vincent Deconinck, a regional official with the Secours Catholique charity, said the migrants have already faced an unkind welcome in France. He said nearly all left the port Friday, and many were now likely to try to sneak across the English Channel illegally.
French authorities offered to provide those who make formal requests for asylum with housing in the nearby city of Arras, while they await consideration of the dossiers. Deconinck said only a few were likely to take up that offer.
"In Calais they weren't able to find a place even to pitch a tent to sleep," he said by phone. "They've been chased from one place to the next, they've been arrested, they have been handed orders to leave the country."
He said some speak English, explaining in part the attraction of Britain. French TV images showed several dozen refugees sitting on the ground, with blue tarpaulins draped over the gangway and displaying protest signs. One read: "We want to start anew in England, pls (please)."
Mael Galisson of Migrant Services Platform, an aid group, said the migrants had occupied the gangway at the Calais ferry terminal since Wednesday, and police moved to evacuate them Friday but backed off after the two Syrians climbed onto the roof and threatened to jump.
For years, migrants have swarmed Calais, hoping to sneak across the English Channel to Britain, which is seen as an easier place than France to make a life.
France and Britain have been among the most vocal critics of the regime of President Bashar Assad in Syria, where at least 100,000 people have died in a civil war.