The French government has vowed to press ahead with its overhaul of the pensions system despite a hardening nationwide strike that will keep transport at a standstill next week amid another round of planned massive street protests.

Four days after at least 800,000 people took part in one of the biggest demonstrations of trade union strength in a decade on Thursday, transport remained virtually at a halt over the weekend as the president, Emmanuel Macron, held talks with ministers at the Elysée Palace on how to diffuse growing tension.

The pro-business president, who has promised to deliver the biggest transformation of the French social model and welfare system since the postwar era, sees his pension reforms as a key test. He has staked his political credibility on refusing to buckle in the face of street protests, accusing previous presidents of lacking the bravery to stand strong. With Macron potentially aiming to run for a second term in the 2022 presidential election, backing down would be to risk losing his support base.

The prime minister, Édouard Philippe, has been pushed to the front to insist the pension reform will go ahead, but after months of gilets jaunes anti-government protests earlier this year, the executive knows that to calm tensions, it must be seen to consult and negotiate rather than force things through in a top-down way.

Édouard Philippe, the French prime minister, delivers a statement about the pensions reform plan at the Hotel Matignon in Paris. Photograph: Benoît Tessier/Reuters

“I am determined to take this pension reform to its completion and I will do this respectfully and I will address people’s concerns about it,” Philippe told the newspaper Le Journal du Dimanche. “If we do not implement a thorough, serious and progressive reform today, someone else will do one tomorrow, but really brutally,” he added.

“The reform we’re putting into place is fair,” the economy minister, Bruno Le Maire, added on Sunday, saying people must work longer to keep the pensions system afloat.

The next few days will be crucial as unions plan another major street protest on Tuesday before the government sets out full details of its pension plans on Wednesday.

The government argues that unifying the French pensions system – and getting rid of the 42 “special” regimes for sectors ranging from rail and energy workers to lawyers and Paris Opera staff – is crucial to keep the system financially viable as the French population ages. But unions see the changes as an attack on fundamental worker rights, and fear people will have to work longer for smaller pensions.

An Ifop poll on Sunday showed 53% of French people supported the strike. Polls earlier this month showed that a majority of French people support pension change but do not trust Macron to do it fairly.

The three main rail unions are calling for strikes to continue this week, with services already virtually at a standstill. In the Paris region, rail operators warned of potentially dangerous overcrowding on the very few trains that would be running.

As hotel unions complained of cancellations and shops said takings were down, businesses feared an open-ended strike which could continue towards Christmas.

The leader of the leftwing CGT union, Philippe Martinez, told Le Journal du Dimanche they will keep up the strike until the withdrawal of the reform plan, which he said contained “nothing good”.