Striking workers poured into streets across France Thursday for a sixth day of demonstrations against a pensions overhaul, putting up a show of defiance after Prime Minister Edouard Philippe said the historic transport stoppage "has gone on for too long".

The rallies came on the 43rd day of a strike that again snarled train and metro traffic and caused misery for millions of commuters in Paris especially.

"It's never too late to make a government back down," Philippe Martinez of the hardline CGT union said ahead of a demonstration at the Montparnasse train station in the capital that included striking teachers, lawyers and hospital workers.

"Our determination is still just as strong" as when the strike was launched on December 5, he said.

Protest numbers were lower than on previous days, however, with the interior ministry estimating the national total at 187,000, with about 23,000 turning out in the capital.

The figures are less than half the count from a week earlier, and way down from an estimated turnout of 805,000 on the first day of the strike.

The action is being led by workers at railway operators RATP and SNCF, who risk losing special early retirement provision under their existing, separate pension scheme which the government is proposing to merge with 41 others to create a single, points-based plan for all.

The number of strikers at the SNCF rose to 10 percent Thursday compared with just 4.3 percent on Monday.

"It's never too late to make a government back down," Philippe Martinez of the CGT union said
"It's never too late to make a government back down," Philippe Martinez of the CGT union said AFP / Christophe SIMON

The moderate CFDT union, France's largest, did not take part in the rally, after welcoming a move by Philippe to temporarily withdraw a measure that would have forced people to work until 64 to qualify for a full pension.

The government says its overhaul will create a fairer, more transparent pension system, but critics say it will effectively require workers in the public and private sectors to work beyond the official retirement age of 62 to avoid curtailed pensions.

"Drop this project once and for all, abandon it and come back to the negotiating table," Yves Veyrier of the FO trade union urged on Thursday.

Philippe's office estimated Wednesday that the strike had cost the SNCF around 800 million euros ($890 million), and the Paris transit authority RATP nearly 200 million euros.

Labour leaders have called for port blockades and other walkouts to amplify their protest, and several polls show public support for the strike hovering at around 60 percent.

The government aims to finalise its bill for approval at a cabinet meeting on January 24 before submitting it to parliament, where a vote is expected within months.

The reform would be rolled out gradually for workers born from 1975, though the government has already granted exceptions to police and military personnel while delaying the shift for Paris Opera dancers, who also have their own pension regime.