China remain top of the medal table at the Tokyo Olympics after an eventful round of action on Sunday that saw the United States and hosts Japan enjoy a golden day.

Having picked up four medals on the first full day of action, China added to their haul with three more golds, one silver and three bronze.

Two of China's golds came in weightlifting, with Li Fabin and Chen Lijun coming out on top in the men's 61kg and men's 67kg, followed by success in the women's synchronised 3m springboard final.

A lot is expected of hosts Japan at these Games and they picked up four golds on Sunday, two of those in judo through Hifumi Abe and Uta Abe.

Yuto Horigome made history by winning the first gold in the men's street skateboarding, while Yui Ohashi finished first in the women's 400m individual medley swimming event.

The United States failed to pick up a medal on the opening day of the Games for the first time since Munich 1972, but they stormed back into contention with 10 medals on Sunday.

That included a gold for Lee Kiefer, who became the first American fencer to win a gold medal in individual foil.

William Shaner and Chase Kalisz prevailed in the men's 10m air rifle and 400m individual medley swimming, meanwhile, and Anastasija Zolotic took taekwondo gold in the women -57kg.

Behind China, Japan and USA in the medal table is South Korea, who doubled their tally of golds thanks to victory in the women's team archery.

Austria, France, Tunisia, Uzbekistan, Australia and the Russian Olympic Committee also got off the mark with their first golds of the delayed 2020 Games on Sunday.

China lead the way with four medals after the opening day of the Olympics, as Richard Carapaz doubled Ecuador's all-time tally of golds in Tokyo.

Yang Qian was the first athlete to strike gold in the Japanese capital, winning the women's 10-metre air rifle competition for China.

Sun Yiwen also claimed a gold medal for China in the women's epee individual fencing event, while compatriot Hou Zhihui came out on top with an Olympic record in the women's 49kg weightlifting.

Pang Wei claimed China's other medal on the opening day, taking bronze in the men's 10m air pistol event.

Carapaz produced a sensational ride to win the men's road race title, becoming the second athlete from Ecuador to win an Olympic gold medal.

Host nation Japan and Italy are joint-second in the medal table with a gold and a silver apiece.

There were three medals for South Korea, including a triumph for Kim Je Deok and An San in the first mixed team archery event.

The United States remain notably absent from the primitive medal table, though, having ended the first day of the Games without a medal for the first time since Munich 1972.