Britain's Queen Elizabeth met US President Joe Biden under the canopy of the world's largest indoor rainforest on Friday as she hosted a reception for leaders of the Group of Seven richest nations, who are holding a three-day summit.

The 95-year-old monarch was joined by the other senior members of the British royal family, with son and heir Prince Charles and his wife Camilla and grandson Prince William and his wife Kate also present.

It was their first major public event together since the funeral in April of Prince Philip, the queen's husband of more than seven decades.

The reception hosted by the queen was held at the Eden Project, whose distinctive bubble-like Biomes house thousands of plant varieties. The project is near the Cornish seaside resort of Carbis Bay on the tip of southwest England, where the G7 summit is being held.

As she sat for a photocall with the world leaders, Elizabeth quipped: "Are you supposed to be looking as if you're enjoying yourselves?", provoking laughter.

"Yes," British Prime Minister Boris Johnson replied. "We have been enjoying ourselves in spite of appearances."

The event was the monarch's first opportunity to meet Biden as US President. He is the 13th US leader she has greeted during her record-breaking 69-year reign.

"Joe and I are both looking forward to meeting the queen," Biden's wife Jill, who joined him at the Eden Project event, had said on Thursday. "That's an exciting part of the visit for us."

They are also due to have tea with the monarch at Windsor Castle on Sunday after the summit has concluded.

Prince Charles also addressed the G7 leaders about his Sustainable Markets Initiative, which aims to involve business and private sector investment in government efforts to combat climate change.

"The fight against this terrible pandemic provides, if ever one was needed, a crystal-clear example of the scale, and sheer speed, at which the global community can tackle crises when we combine political will with business ingenuity and public mobilization," the prince told them.

"Ladies and gentlemen, we are doing it for the pandemic. So if you don't mind me saying so, we must also do it for the planet," said Charles, 72, who has spent much of his life campaigning on environmental issues.