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.