LONDON: Usain Bolt acknowledged on Friday that repeating his staggering gold medal achievements in Rio in 2016 would be a tough mission as his younger rivals target his legacy.

Bolt wrote himself into the history books when he retained his 200m title on Thursday, following his successful defence of his 100m crown earlier in the week.

With his double golds in London, the 25-year-old Jamaican bettered the record of US track legend Carl Lewis, who won three golds and a silver in the sprints at the 1984 and 1988 Games.

But he warned that repeating his feats at the 2016 Games in Rio de Janeiro could be a tough call.

“I think when I get to 30 I will be thinking about retiring,” Bolt said.

“I'm not ready to retire yet. I love this sport, I have got all my success through this sport. I got all my fans through this sport.

“Track and field is way too hard. Yohan Blake is running 19.4 already, he's running 19.7, so in the next four years he's going to be firing. I think I want to get out before he starts running too fast.”

Blake, tipped as Bolt's natural successor as the world's fastest man, won silver in the 200m behind Bolt's 19.32sec, with a third Jamaican, Warren Weir, claiming bronze.

“I think it's going to be a hard mission,” Bolt said of racing in Rio.

“Both these guys are 22 - I'm going to be 30, they are going to be 26.

“I think I've had my time. In life everything is possible, but for me this is going to be a hard reach.”

But while Bolt's apparently laidback demeanour is the only thing many people pick up on, he said that he had only achieved the unique “double-double”through intricate planning and hard training.

“To have set a goal for yourself for years to become a legend, you can't really explain what that means. It's not going to hit you until you sit down and think about it,” said Bolt.

“Those are the things that will bring tears to your eyes. I know that when I sit down and think about the struggles that I've been through over the seasons, it will be emotional.

“I have been saying this for the last three years, that I want to become a legend, and I've done it. Now im going to sit back and relax and see what I'm going to do.”

Bolt said that training partner Blake had contributed massively to his performances in the British capital, where his very presence wowed the 80,000-capacity Olympic Stadium.

“I said to him, 'you came around the wrong time, these next two years are mine'. I had to show him these next two years are mine,” Bolt said of their build-up to the Games under the tutelage of coach Glen Mills.

“But he kept pushing me. It's what I needed.”

Bolt added: “After the Olympic trials where Yohan beat me, there were a lot of people doubting me, but that is good because you know who are your true friends and who is going to support you.”

“That (victory) was for all the doubters. That was for them, to tell them to stop talking, I'm a legend.”

Bolt stressed that any celebrations will be on hold until after the 4x100m relay.

“All I have to do now is go home and rest, I have got the 4x100m on Saturday. But after that I'm going to party like it's my birthday!”