Eight big unions are taking part in the strike, which is disrupting schools, public transport and oil refineries.

Protests are taking place across France, after a first day of action attracted more than a million people.

Half the country's teachers were reported to have joined the strike.

The Macron government is pushing ahead with its pension age reforms in the face of opinion polls that suggest two-thirds of voters are opposed to the changes, which begin their passage through National Assembly next week.

Without a majority in parliament, the government will have to rely on the right-wing Republicans for support as much as the ruling parties' own MPs.

Far-left leader Jean-Luc Mélenchon said France was at a crucial point and predicted an even greater number of protesters than on the first day of action on 19 January. Street protests are expected in at least 200 towns and cities and a reported 11,000 police have been deployed to cover the demonstrations.

Ahead of the main protest in Paris, big turn-outs were reported in Toulouse, Marseille and Nice in the south, and Saint Nazaire and Nantes in the west.

There was severe disruption to transport, with one in three high-speed trains running and only two driverless metro lines operating normally in Paris. Large crowds were reported on one of the main overground lines in the capital.

The CGT union said at least three-quarters of workers had walked out at the big TotalEnergies oil refineries and fuel depots. Power plants reported reduced production after workers went on strike at the main electricity company EDF.

One of the main teachers' unions said some 55% of secondary school teachers had walked out. High school pupils staged protests outside some schools and students said they would occupy Sciences Po university in Paris in support of the strikers.

"A lot of French people feel that working is more and more painful. It's not that they don't want to work, they don't want to work in these conditions," Sciences Po political scientist Bruno Palier told the BBC.

The government has indicated it may move some way on the detail of the reform but has refused to give in on the main thrust of the raising the retirement age by two years to 64.

"Any kind of reform that is going to ask people to work longer will be unpopular, but we've been elected on this reform," said Christopher Weissberg, an MP in President Macron's Renaissance party.

At 62, France's retirement age is lower than most other countries in Western Europe. Italy and Germany have moved towards raising the official retirement age to 67, while Spain's retirement age is 65 and in the UK it is 66.

In France, very few workers have personal pensions linked to capital investments, but there are now only 1.7 workers paying into the shared pension fund per person in retirement.

"We have a universal system, and the system has to pay for itself. If not, it's weakening and if it's weakening, at some point, people will lose their pension," Mr Weissberg warned.

Economist Prof Philippe Aghion said the reforms were necessary because France had a structural deficit of some €13bn ($14bn; £11bn) and raising the retirement age would also help increase the rate of employment in France.

"That will give the government credibility to make some investments that it needs to make in schooling, in the hospital system that it needs to improve, and more investment in innovation and green industrialisation," he said.