French fishermen started blocking access to ports on Friday amid a row over post-Brexit fishing licences.
The blockade began at the port of Saint-Malo in the morning, with actions also planned later on Friday in Ouistreham and Calais.
French fishermen will furthermore block freight trucks coming to the Channel Tunnel terminal for "a few hours," said Gérard Romiti, the chairman of the French national fisheries committee, at a press conference.
"We don't want handouts, we just want our licences back," he said.
As part of the post-Brexit divorce agreement signed by London and Brussels, European fishermen can continue to fish in British waters provided they can prove they were fishing there before.
France has obtained more than 960 licences for fishing in British waters and near the Channel Islands but is still asking for more than 150 authorisations, the sea ministry says.
"It has been eleven months...the patience of professionals has limits. We hope that this warning shot will be heard," said Romiti, who said he would not rule out future action.
He warned that the movement was in response to a "provocative" and "humiliating" attitude of the British.
The British government on Thursday said it was "disappointed" by the move.
"We are disappointed with the threats of protests. It will be up to the French to make sure that illegal acts are not committed and that trade is not affected," a Downing Street spokesman said.