Usain Bolt delivered what may well go down as the greatest track performance in athletics history here in Beijing today, as he smashed the world 200 metres record and completed a unique golden world record sprint double.

It did not seem feasible that the 21-year-old Jamaican could surpass his breathtaking landmark 100m triumph of Saturday but, again redefining the limits of human endeavour, he completed half a lap in an unreal 19.30 seconds, thus annexing the record they said could not be broken.

By erasing Michael Johnson's 12-year-old mark of 19.32sec from the book, Bolt became the first man ever to achieve the golden sprint double at an Olympics with two world records.

Eight men had previously achieved the double, the last being Carl Lewis in 1984, but none had come near to completing the feat with such ground-breaking performances. For if Bolt's 9.69sec run in the 100m, even while managing to do a little showboating during the race, was mind-blowing, this was just out of this world.

So blown away was the youngster as he glanced at the clock after completely obliterating the field that he fell on to his back afterwards in astonishment. Record holder Johnson probably felt the same way up in the BBC eyrie after earlier predicting that his record would survive the evening.

Most felt he was right, because his Atlanta tour de force was so amazing, something to match Bob Beamon's incredible Olympic-winning long jump of Mexico City in 1968, that it would not be beaten for generations.

Yet ultimately it could not resist the amazing 'Lightning' Bolt, who had promised there would be no messing around in tonight's race - his best distance - and even having to run into a headwind of 0.9m/s couldn't stop his charge to history.

Earlier in the day, Johnson had said: "I don't think he'll break it here. I will be shocked if he does ... but then I didn't think he was going to run 9.69 either."

Equally shocked was Britain's Christian Malcolm, who had a track-side view of Bolt's achievement while finishing in sixth place behind the Jamaican.

He said: "I am in shock, what can you say [about Bolt]? When you are running-against someone like that you just have to keep going. He will have a bad day some time."

The Welshman, who finished fifth in Sydney eight years ago, insisted he would take great heart from reaching today's final.

The 29-year-old added: "I am healthy and made the final and the most important thing is that I am injury-free."

Meanwhile, there was late drama for Britain as Natasha Danvers claimed an unexpected bronze medal in the women's 400m hurdles. The race was won by Jamaican Mellanie Walker in 52.64sec.

Earlier in the day, Britain's Michael Rimmer survived a real scare in the first round of the 800m heats.

The Liverpool athlete, 23, who is studying for a history degree at John Moores University, looked like he hadn't done his homework on the rest of the field as he was passed by Poland's Pawel Czapiewski and South Africa's Mbulaeni Mulaudzi at the start of the home straight.

Spain's Miguel Quesada also joined the fray as the run-in turned into a fourway fight for the two automatic qualification spots for the semi-finals.

But Rimmer kept battling and showed great endeavour to move wide and muscle his way back into the contest. With a final burst of speed, he just managed to get his chest in front as the line approached, winning the heat in a time of 1min 47.61sec.

Rimmer will be joined in the next round by Mulaudzi, who edged out Czapiewski in a photo for second.

Rimmer is Britain's only representative in the 800m and it was a similar story in the 5,000m until Mo Farah crashed out after finishing only sixth in his heat.

The Twickenham athlete, 25, led for much of the latter part of the race but was outgunned on the last lap and failed to make the final as a fastest loser.

The heat was won Edwin Cheruiyot Soi of Kenya, while 10,000m champion Kenenisa Bekele of Ethiopia stayed on course for a distance double by qualifying comfortably in third place from his heat.

Off the track, it emerged today that Lyudmila Blonska, the Ukrainian athlete who won silver in the women's heptathlon, is facing disciplinary action after failing a drugs test.

It is understood Blonska, who has previously served a two-year ban for drugs, tested positive for an anabolic steroid.

The case is expected to come before the International Olympic Committee's disciplinary commission and executive board, which meet tomorrow.

Blonska has qualified for the women's long jump final, which also takes place tomorrow.

After Blonska's silver medal Britain's Kelly Sotherton, who finished fifth in the event, called for a worldwide policy to prevent drug cheats from returning to compete in the Olympics.

Reacting to today's news, Sotherton added: "I'm totally not surprised. I've been saying all along that she got caught doping when she was scoring 6300 points, how can she not be doping and scoring 6800?

"I have not seen any of her results since early June and then she comes out here and is producing good performances, which was suspicious.

"If the B sample comes back positive then that's a life ban, which will bring an end to the saga - hopefully she will be finished.

"I'm happy I've moved up one place, but I'm still disappointed with my performance."