The postponement - at Macron's request - will be a major embarrassment to the French leader, who had hoped the monarch's visit would mark a symbolic step in the two countries' efforts to turn a page after years of poor relations over Britain's exit from the European Union.

Charles had been due to travel to France on Sunday for three days - in what would have been his first state visit since he succeeded his mother Queen Elizabeth as British monarch in September - before moving on to Germany.

That itinerary had been seen as a win for Macron, who has sought to position himself as Europe's de facto leader. Charles' trip would have included a lavish banquet at the Palace of Versailles.

"You can see the situation linked to the protests," Macron told a news conference during a visit to Brussels.

He added that "it would not have been serious" to host the state visit after unions announced a nationwide day of strikes and protests for Tuesday.

"Common sense and friendship pushed us to propose to postpone (the visit)."

A British government spokesperson said the decision was "taken with the consent of all parties" after Macron asked the British government to postpone the visit.

The last-minute scrapping of the visit will pile further pressure on Macron to find a way out of a crisis over his plans to raise the retirement age by two years to 64, which has seen some of France's worst unrest since the "Yellow Vest" rebellion of 2018-2019.

The Elysee said it hoped the visit would be rescheduled in the coming months.

"There were calls on social networks to disrupt the king's visit, to take action, so we didn't want to take any risks," a French source close to the matter said.

A Buckingham Palace source said Charles' visit to Germany will go ahead as planned.

The king and his wife, Queen Consort Camilla, looked forward to rescheduling the visit to France "as soon as dates can be found", a Buckingham Palace spokesperson said.

STREET BATTLES

Black-clad anarchists fought street battles with police for several hours in the French capital on Thursday, ransacking a McDonald's restaurant, smashing up bus shelters and setting alight mounds of garbage that have piled up during strikes.

In Bordeaux, at the heart of one of France's best-known wine growing areas and where Charles had also been expected to visit, protesters set alight the entrance to the city hall.

"He's right not to come right now," said architecture student Mathias Sainte Agathe. "There are protests and strikes everywhere."

Weeks of protests over Macron's pension plans escalated and became more violent after his government pushed the legislation through parliament last week without a vote. His government lacks a clear majority.

The president has insisted the pensions changes are essential to keep the system funded.

Hard-left leader Jean-Luc Melenchon, who earlier this week said now was "not the right time" for Charles to come, welcomed the cancellation of the visit.

The left-wing opposition and some protesters often mockingly portray Macron - who began his second term in office last year - as a would-be monarch.

"The meeting of the kings in Versailles is broken up by popular censure," Melenchon tweeted.

But not all were happy that the visit was postponed.

"Why is he not coming? I don't understand," jewellery worker Razmig Kertechin said in Paris.

"We're not bad people. It's just the way it is, it's the freedom (to protest). I don't know, that's weird."