France's labour unions appealed to President Emmanuel Macron on Tuesday to “hit pause” on his plans to raise the legal retirement age as a new round of demonstrations and strikes got under way and the authorities deployed thousands of police.

Millions of people have been demonstrating, largely peacefully, and joining strike action since mid-January to show their opposition to Macron's plans to make most of them work an extra two years to 64.

But public frustration has evolved into broader anti-Macron sentiment.

The protests have intensified since the government used special constitutional powers to bypass parliament on a final vote on the pensions bill almost two weeks ago, bringing scenes of chaos reminiscent of unrest by supporters of the yellow-vest movement during Macron's first term as president.

Interior Minister Gerald Darmanin on Monday said authorities had seen a trend towards more violence directed against the state and were anticipating a“very serious risk to public order” at demonstrations expected in cities including Paris, Lyon, Nantes and Bordeaux.

A total of 13,000 police will be deployed during the protests throughout the day, more than ever before, Darmanin said.

Motorways in several French cities were blocked on Tuesday morning, and strikes in the transport, aviation and energy sectors continued to disrupt parts of public infrastructure.

About 17 per cent of all fuel stations in France were missing at least one product as of Monday night, France's petroleum association UFIP said, citing French energy ministry data.

Student union UNEF said the entrances to around 20 universities including Sciences Po and parts of the Sorbonne in Paris as well as institutions in Lyon, Nice and Toulouse were also blocked.

Laurent Berger, the head of France's largest union, the CFDT, urged Macron to show “a gesture of appeasement” to calm things down.

"It is necessary to hit pause on the measure,” Berger said in remarkes which were echoed by Philippe Martinez of the CGT union as both leaders suggested Macron should appoint mediators to the conflict.

Berger said there had been some attempts at talks between union leaders and the government in recent days - which had failed.

Macron, who promised to deliver a pensions system reform in both of his presidential campaigns, says the move is needed to keep the country's finances in balance. Unions and opposition parties say there are other ways to do that.

Meanwhile, police were preparing for more protests.

Laurent Nunez, president of Paris's Prefecture de Police, told France Inter radio that security agencies believed more people intent on violence could join the protests and police had to be ready.

"We are talking about individuals which often are being monitored by intelligence services ... and we are very vigilant about their presence,” Nunez said.