French unions have warned there will be no "Christmas truce" in its dispute with the government over pension reforms which has led to weeks of nationwide strikes.

Power was cut to 100,000 homes and offices, schools were closed, roads blocked and public transport crippled on Tuesday as protests were staged across France in support of the general strike over pension reform.

Flares and union flags filled streets all over the country on the 13th day of industrial action against the government's plan to raise the retirement age to 64.

France's interior ministry said roughly 615,000 protesters took part whereas the CGT union said the number was 1.8 million.

With only one-in-four high-speed trains running and half of Paris metro lines closed, the commute to work was a misery for millions.

Tourists found attractions closed, including the Eiffel Tower.

Workers from the CGT carried out what they called “targeted” blackouts on electricity networks around Lyon and Bordeaux, further disrupting travel.

No breakthroughs in sight

Despite the union's hardline stance, Tuesday did not see an uptick in street protests they had hoped for to persuade Emmanuel Macron's government to drop the reforms.

In Paris, police fired tear gas and charged to disperse demonstrators from the Place de la Nation, though there was none of the rioting and looting that marked the "yellow vest" protests against high living costs late last year.

The unions spearheading the industrial action said in a joint statement that Tuesday's marches across France reflected a "massive rejection" of Macron's planned pension system overhaul and called for the reform to be abandoned.

"If it is not pulled, there will be no truce," the unions said.

Why workers are striking

Many of the country's largest unions say the Macron reforms will led to an erosion in the pension protections for French workers.

"We have one of the best pension systems in the world, if not the best. However, the President of the Republic decided, by pure ideology, to destroy it," the General Confederation of Labour (CGT) wrote in a statement calling for workers to strike.

The Paris metro was overcrowded — if it ran at all AP

CGT leader Philippe Martinez said it was up to the government to pull its new reform plan if they did not want the strike to impact the upcoming winter holiday season.

But the secretary-general of the CFDT union, Laurent Berger, said it is elements of the plan they want to change.

"It is especially those who started working at a young age and those who find themselves unemployed at the end of their career who will be penalised," Berger said in a statement.

But the government has shown no sign of folding on its plans which are meant to de-complexify the system, by transforming it to a single point-based system.

"I am completely determined to carry out this transformation because I believe it is deeply just," Philippe said while unveiling the plan last week.

Government spokesperson Sibeth Ndiaye said that the government would host meetings with unions and organisations on Wednesday.

Rail workers, in particular, have been striking over proposed changes that include scrapping industry-agreed retirement plans in favour of a universal pension system.

Protesters were further enraged by the revelation that the architect of the reforms, High Commissioner for Pensions Jean-Paul Delevoye, had failed to declare income from 13 paid and volunteer roles on his conflict of interest declaration when he entered government two months ago.

His resignation on Monday has failed to satisfy unions.

Macron has nominated Laurent Pietraszewski, a deputy from En Marche from the Nord department, to take his place.

Read more:How can France best reform its pensions system?

It is not only about retirement. Health workers are planning on joining the strikes to protest a lack of funding for treatment. They're also planning to mobilise on December 20.

Teachers also came out in force on Tuesday, leading to a strike rate of 25.05% in primary schools and 23.32% in colleges and high schools, according to the government. The true figure was 50% and 60% according to the unions.

Three days before the Christmas holidays, it is a very strong mobilization which reflects the level of exasperation of the teachers. Régis Metzger Co-secretary general of Snuipp-FSU, the first primary union

Marches in cities

French railway operator, the SNCF, said only 25% of high-speed trains ran on Tuesday, and only 33% would run on Wednesday.

Passengers on regional trains should try carpooling to reach their destination, SNCF said in a statement.

In Paris, protests filled Place de la République, Place de la Bastille, and Place des Nations. Eight metro lines were closed and the rest were overcrowded.

Delays and cancellations hit airports as well, with the civil aviation authority asking airlines to reduce air traffic into Paris Orly airport by 20%.