Olympics legend Nadia Comaneci held the 2012 torch aloft over London on Saturday as the flame began a seven-day tour of the host city that will culminate at the Games opening ceremony.

Olympics organisers hope that with the flame now in the British capital, attention will turn towards sport and the final countdown to the Games -- and away from the security and transport fears that dogged the last week.

Comaneci, the perfect 10-scoring Romanian gymnast who won five gold medals over the 1976 and 1980 Olympics, passed the flame on to British ex-NBA basketball star John Amaechi atop the North Greenwhich Arena -- the former Millennium Dome -- which will host the artistic and trampoline gymnastics as well as the basketball finals.

The flame spent the night safe in the Tower of London, where the British sovereign's ceremonial jewels are kept, following a dramatic arrival in the city Friday, a week ahead of the opening ceremony on July 27.

It was flown in on a Royal Navy helicopter and lowered to the ground by a marine commando carrying it in a miner's Davy lamp attached to his waist.

The final seven days in London are the last legs of an 8,000-mile (12,800-kilometre) journey around Britain that has taken the flame within an hour's travel time of 95 percent of the British population, taking in famous sports venues, historic sites and places of outstanding natural beauty.

Its 36-mile (58-kilometre) tour Saturday around eastern London started at the Royal Observatory, Greenwich, located astride the world's prime meridian.

Natasha Sinha, 15, started the relay at 7:20am, or 0620 Greenwich Mean Time.

Robin Knox-Johnson, the first person to sail solo non-stop around the world, carried the torch on a lap of the nearby Cutty Sark, the tea clipper ship which has undergone a £50 million (64 million euro) renovation following a fire in 2007.

Comeneci then took the flame to the top of the North Greenwich Arena.

"I'm happy that I had the honour to carry that in such an unusual way," the 50-year-old told BBC television on top of the 20,000-seater indoor venue.

"London is doing great. Everybody is ready for it, everything is prepared, some of the athletes already arrived and they are excited to start to compete and the entire world will be here so there's not a better place to be right now."

British triple jumper Phillips Idowu, the Beijing 2008 silver medallist, carried the torch through the Westfield shopping centre at the edge of the Olympic Park and appeared overwhelmed by the support.

"Being born, raised and schooled in east London, having the opportunity to carry the Olympic torch in the home Games in front of my east London people... It's an amazing feeling. I'm full of emotion," he said.

Inside the Olympic Park, competitors were getting used to their new surroundings, while the Australian women's hockey team were out on the practice pitch.

There was even sunshine -- a welcome sight after a week of miserable weather.

The oldest and youngest torchbearers were on Saturday's relay, with 101-year old marathon runner Fauja Singh and schoolboy Chester Chambers, 12, taking part.

Footballer Fabrice Muamba, who suffered a heart attack during an FA Cup match in March, will be the last torchbearer of the day.

Meanwhile a 17-year-old boy was to appear in court following an alleged attempt to snatch an Olympic torch on Friday as it went through Gravesend, east of London.

Last week's headlines were dominated by Britain having to send an extra 3,500 troops to the Games -- taking the full deployment to 17,000 -- after private security firm G4S admitted they could provide the full contingent of guards.

London Games organisers said they would be allocating extra tickets to the service personnel, some of whom should have been on leave after returning from Afghanistan.

"We are hugely grateful to the troops for their support, and they are doing a great job," a spokesman said.