King Charles III on Friday arrived in France's southwestern city of Bordeaux on the final day of his state visit, putting the environment at centre stage in a region famed for its vineyards but also hit by climate-induced wildfires.

The 74-year-old British head of state is wrapping up a three days of diplomacy aimed at forging closer cross-Channel links after Brexit but also closer cooperation on environmental issues, his lifelong passion that are now top of the global political agenda.

Crowds of Union Jack-waving well-wishers gathered outside Bordeaux city hall to welcome Charles and Queen Camilla as they arrived after landing at the city's airport, AFP correspondents said.

Bordeaux is well-placed to illustrate the point hammered home throughout the visit about Britain and France's shared personal, political and cultural history.

It became a British possession in 1152, when the future English king Henry II married Eleanor of Aquitaine, effectively beginning three decades of English dominance in the region, until the end of the Hundred Years' War in 1453.

The British influence remains: some 39,000 British expats live in Bordeaux -- the highest number in France.

- 'Iron Duke' -

Charles, accompanied by his wife Queen Camilla, 76, had been due to visit France in March but civil unrest over unpopular pension reforms forced the trip to be postponed at the last minute.

His rescheduled tour, including a ceremonial welcome at the Arc de Triomphe, a glittering state dinner at the Palace of Versailles and a landmark address at the Senate, has been largely well-received.

The warmth of Charles's relationship with President Emmanuel Macron was clear, with the king set a slightly more informal atmosphere than would have been the case under his late mother Queen Elizabeth II.

On Thursday, Charles called for a new Franco-British partnership for the environment -- an alliance for sustainability -- as part of a wider effort to repair frayed political ties caused by Brexit.

Speaking to lawmakers in the upper chamber of parliament -- a first for a British monarch -- he notably called climate change "our most existential challenge of all".

Some commentators in the UK interpreted that as coded criticism of Prime Minister Rishi Sunak, who this week rowed back on the government's net zero commitments.

But Charles has for a long time warned about the need to protect the environment for future generations, and he praised efforts by governments in both London and Paris for making moves to address the issue.

Before it was fashionable, he created an organic garden at his Highgrove estate in western England and has long published his household's carbon footprint.

The Aston Martin DB6 he has owned since 1970 has been converted to run on bioethanol from surplus English white wine and whey from cheese-making.

On his visit, Charles is to celebrate defence ties between the two NATO allies on British frigate HMS Iron Duke, ironically named after the Duke of Wellington, the British commander who defeated Napoleon at the battle of Waterloo in 1815.

In a key engagement of the day, Charles will then go on to visit a research centre looking at how forests are adapting to climate change.

Huge fires, fuelled by drought and high temperatures, ripped through the Gironde region near Bordeaux last year.

His last stop before heading home is a visit to Chateau Smith Haut Lafitte vineyard, which has become a model of sustainable practice.

The vineyard, founded in the 14th century and named after Scottish former owner George Smith, uses organic compost and carbon dioxide recycling technology, shunning pesticides and herbicides.