The United States set a new world record time as they powered to Olympic gold in the women's 4x100m medley relay on Sunday with Australia taking silver and China bronze.

The win ensured that the US finished top of the medals table in swimming with eight golds to Australia's seven.

The Americans hit the wall in 3min 49.63sec, beating the previous record of 3:50.40 set by the US team at the 2019 world championships.

It was the perfect end to a strong Games for the American women with the team of Regan Smith, Lilly King, Gretchen Walsh and Torri Huske all adding to their medal haul.

Canada's Kylie Masse grabbed an early lead in the opening backstroke leg but Smith handed over to King with the Americans in the lead.

King extended their advantage over the Canadians with the highly-fancied Australian team in third.

Walsh, silver medallist in the 100m butterfly, opened up an insurmountable lead before Huske, who won gold in the 100m fly and silver in the 100m freestyle, made sure of the world record and the gold with a strong anchor leg.

The US lead the medal table in this event with 11 golds and have won a medal at every Olympic Games, with the exception of Moscow 1980, which they boycotted.

"We've brought (the record) down a lot, so it's really cool to continue to be a part of that relay and watch it get faster and faster and faster, (with) pretty much the same people," said King.

Walsh said the team had been boosted by seeing team-mate Bobby Finke break the world record in the 1500m freestyle.

Finke's win also had tied the US and Australia on seven swimming golds each before the medley victory ensured top spot for the Americans.

"Bobby's swim was electric, and that was amazing, and he definitely that got my energy going for the relay, so I was pumped to hopefully assert that lead and get the gold," said Walsh.