Thousands of people turned central London red, white and blue on Saturday, with a sea of Union Jack flags lining the streets for the coronation of King Charles III.

While the coronation service itself promises to be a sombre and sober affair, a celebratory atmosphere was building in the British capital and beyond.

On The Mall outside Buckingham Palace, the most fervent royal fanatics have already got the party started, with some camping out for days to secure a prime spot for the historic event.

On Whitehall, too, crowds were building on the street leading to Westminster Abbey, cheering marching bands as they passed.

The Union Jack is omnipresent, being waved on flags, emblazoned on T-shirts and painted on people's faces.

There are many crowns too, from simple home-made headgear to sophisticated ermine and purple velvet pieces.

- 'Good vibe' -


Among the early birds was Caryl Hall, 55, and her teenage children.

"I'm excited. There's a good vibe, good atmosphere -- friendly, happy, patriotic," said Hall, draped in a flag with a plastic crown on her head.

"It was hard to wake up the teenagers but this is part of history, we don't know if we'll see another one," added the South African, who was standing on a small stool to get a good view.

Lawyer Henry Bokenham, 45, called the atmosphere "expectant, anticipatory, quietly excited, reverent".

"It's just worth getting up early and get a good spot," reasoned London-born Bokenham, sporting a woollen Union Jack hat with a pompom.

Torrential downpours on Friday failed to dampen spirits, but more bad weather is forecast for Saturday.

Hillary, 72, and her daughter Jo, 47, were well prepared as they caught an early train to join the crowds.

"It's living history. He is never going to be the queen (Elizabeth II) but he is our king and today we just want to celebrate," said Hillary, who only gave her first name.

The pair were packed up with Union Jack hats, flags and picnic chairs, but in true British fashion were worried about the weather forecast.

Early arrivals also have to deal with practical problems such as going to the toilet and bagging food and drink.

"It seems pretty organised, let's see how the day progresses -- there's food, coffee," said Bokenham.

"Things aren't too bad at all, it seems very civilised."

- Celebration -


Many have flown in from abroad, including Christine Wilen, a retired nurse from Niagara Falls in Canada.

"I made the trip for the coronation," the 55-year-old, kitted out in the colours of her native Canada, told AFP.

"I'm very excited to be here, to be part of this history. I've always been a monarchist," she added.

Recent polls indicate waning support for the royals, especially among younger people, and at Trafalgar Square, republicans holding "Not My King" signs gathered to protest.

But they were outnumbered by monarchists, including Caba Mendes, 21, from London.

"It's a great day for the country, I can't wait," he said while holding his phone with a selfie stick for the procession on The Mall.

Helen Rimmer, who travelled from Cumbria, northwest England, on Friday night, secured her spot on Whitehall at 4:45 am.

"It's a very special occasion, especially for our country and the Commonwealth. It's the atmosphere, just everything about it really. It's just a big celebration. It's great."