King Charles, his sons William and Harry and other senior royals joined a solemn procession behind the coffin of Britain's Queen Elizabeth II through the silent streets of London on Monday, following a state funeral of matchless pageantry at Westminster Abbey.

Hundreds of thousands of people crammed into central London to witness the ceremony attended by leaders and royalty from across the globe, a fitting end for Britain's longest-serving monarch who won widespread respect during 70 years on the throne.

Her flag-draped casket was pulled on a gun carriage the short distance from Westminster Hall to the Abbey by 142 sailors with arms linked. A bell tolled and bagpipes skirled.

Pin-drop silence fell over London's Hyde Park nearby as thousands of people, who for hours had picnicked and chatted, went quiet the second the queen's coffin appeared on screens erected for the occasion.

Shortly before, hundreds of armed personnel in full ceremonial dress had marched in a historic display of kilts, bearskin hats, scarlet tunics and brass bands.

Inside the abbey, lines of scripture were set to music that has been used at every state funeral since the early 18th century. Among those walking behind the casket was the queen's great-grandson and future king, nine-year-old Prince George.

The 2,000-strong congregation included some 500 presidents, prime ministers, foreign royal families and dignitaries.

Justin Welby, the Archbishop of Canterbury, told the congregation that the grief felt by so many across Britain and the wider world reflected the late monarch's "abundant life and loving service."

"Her late majesty famously declared on a 21st birthday broadcast that her whole life would be dedicated to serving the nation and Commonwealth," he said.

"Rarely has such a promise been so well kept. Few leaders receive the outpouring of love that we have seen."

Among the crowds who came from around Britain and beyond, people climbed lampposts and stood on barriers and ladders to catch a glimpse of the royal procession - one of the largest of its kind in modern history in the capital.

Some wore smart black suits and dresses. Others were dressed in hoodies, leggings and tracksuits. A woman with dyed green hair stood next to a man in morning suit as they waited for the procession to begin.

Millions more watched on television at home on a public holiday declared for the occasion, the first time the funeral of a British monarch has been televised. Elsewhere, London's normally bustling streets were deserted.

Ben Vega, 47, a nurse from the Philippines standing at the back of the crowd on a stool, said he was a royalist.

"I love pageantry. I love how the British do this," he said. "I'm from the Philippines, we don't have this, we don't have royal families. It's a sad day for me. I've been here 20 years. I saw the queen as my second mum, England as my second home."

Queen Elizabeth died on September 8 at her Scottish summer home, Balmoral Castle. (Reuters)