The 'yellow vest' protest movement – which has been attracting small numbers at recent demonstrations, declared a 'day of anger' and Thursday and matched alongside the huge trade-union organised strike demonstrations in Paris and other cities.

But on Saturday they will return to their usual weekly day of protest and police in Paris fear further violence.

On Thursday several hundred masked, black-clad rioters belonging to the extreme-left “Black Bloc” group infiltrated the protest, smashing windows and setting fires in the Place de la République, the half way point of the unions march.

And there are fears they could be out again on Saturday in the capital.

The main 'yellow vest' march is on a long route that runs from Metro Bercy, near the French finance ministry,  through Denfert Rocheraut to the Porte de Versailles on the southern edge of the city. There is another demonstration that calls on protesters to meet at Montparnasse at noon.

French newspaper Le Parisien quotes an unnamed government source saying that there are security concerns.

A security expert told the newspaper: “It's going to be a tense moment, with a risk of violence. On encrypted networks and internet loops, there are already calls: see you on the 7th!”

On the one-year anniversary of the 'yellow vest' movement in Paris a group of about 200 'Black Bloc' smashed up the Place d'Italie.

Usually when there are fears of violence on demos Metro lines are suspended, but this weekend very few Paris public transport lines will be running because of ongoing strike action.