The team of Tianna Madison, Allyson Felix, Bianca Knight and Carmelita Jeter blazed round the track in 40.82 seconds, beating East Germany's record of 41.37, which had stood since 1985.

Jamaica was second in a national record time of 41.41, with Ukraine third in 42.04 and Nigeria fourth.

The USA team had failed to reach the final at the Beijing Olympics.

But after qualifying fastest for the 2012 final, they led from the start on a balmy night in east London.

Madison gave the US an electric start, with Felix and Knight maintaining the lead before 100m silver medallist Jeter stormed down the straight to capture the gold.

BBC SPORT