The Olympic flame was held high above the British capital as it took flight on the London Eye.
Seventeen-year-old Amelia Hempleman-Adams held the flame aloft as she stood on top of one of the capsules.
Hempleman-Adams, who at 16 became the youngest person to ski to the south pole, said carrying the torch was an exhilarating experience.
"It was amazing, and you get out at the top and you see across the whole of London, just an amazing view and an amazing feeling just having the flame in front of you," she said.
In the coming days, the torch will be carried around London's religious, political and royal landmarks, culminating in the lighting of the Olympic cauldron in east London.