A double rainbow arched over the London skyline shortly before well-wishers fell into stunned silence as the palace lowered its Union Jack flag to half-staff, signifying the death of the monarch.

“We’ve grown up with her always being there,” consultant Margaret Parris said, tears welling up in her eyes.

She had travelled 32km to the palace after hearing earlier in the day that the

Elizabeth died peacefully at her home in Scotland, aged 96.

Her eldest son Charles, 73, is now King.

The mood on the esplanade in front of Buckingham Palace was very different three months ago, when the Queen appeared on the balcony to huge cheers from revellers enjoying her Platinum Jubilee celebrations, which marked her 70 years on the throne.

On Thursday, a sense of anxiety turned to shock when news of her death was announced.

The palace posted an official notice on the gates outside, which Londoners and tourists alike pressed forward to see.

Thousands more people started to arrive, some carrying flowers.

“It felt like history in the making, so we rushed over to the palace. Quite something for a holiday,” said Nabeel Dockrat, 26, a tourist from South Africa.

The sense of history passing was felt just as keenly in Edinburgh, Scotland’s capital.

“It’s one of those days like ‘where were you when JFK was shot? Where were you on 9/11?’,” Laura McGee, 37, a solicitor from Glasgow, said.

“I think people appreciated, whether you are a royalist or not, that she really gave an amazing service and a lot to the country.”

At Buckingham Palace, 22-year-old student Adam Wilkinson-Hill arrived with a bunch of white lilies on behalf of himself and a group of his friends who could not be in the capital.

“It’s a massive shock to the nation,” he said.

-AAP