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 were 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.
"I knew that these girls were going to run their hearts out," said Jeter. "I knew we were running fast.
"There was a cloud hanging over us with people saying 'they can't do this, they're going to drop the stick' but we did it."
The Jamaican quartet featured 100m champion Shelly-Ann Fraser-Pryce and bronze medallist Veronica Campbell-Brown, but they could not match the fierce pace of the world champions.
"It's an honour to be part of this team," said Felix, the 200m champion. "Who would have thought that we would have had a world record tonight? It's amazing. Our names are going down in history."

It was the second track world record at London 2012 after Kenya's David Rudisha set a new men's 800m mark on Thursday.