The G7 gathered in Japan should "mind its own business rather than pointing fingers," Chinese state media said in an editorial Thursday.
Summit host Japan had a "hidden agenda," according to the piece in Beijing's state-owned Xinhua news agency, "to meddle in the South China Sea issue."
The group of seven leading industrialized "should mind its own business rather than pointing fingers at others and fueling conflicts," the commentary said.
China claims a wide swathe of the sea, overlapping with territory claimed by Vietnam, the Philippines, Brunei, Malaysia and Taiwan.
G7 countries including the US have expressed concern over escalating tensions, which have seen Beijing reclaim land and build installations including airstrips on shoals in the disputed area.
The editorial called Japan "a complete outsider in the South China Sea disputes," that nonetheless "seems to be attempting to take advantage of its G7 summit host status and draw more 'allies and sympathizers' to isolate China on this issue."
Japan's own main territorial dispute with China is in the East China Sea over the Senkaku, or Diaoyu, Islands off Taiwan.
Xinhua said Tokyo's agenda-setting reflected a "lingering Cold War mindset" in line with the US "pivot to Asia" and would aggravate regional tensions.
But it said the "obviously provocative action" would prove futile "as it exceeds the G7's current influence and capability."
G7 leaders are meeting for two days in the Japanese coastal city of Shima where they are expected to voice opposition to island construction and militarization of outposts in the South China Sea, without explicitly naming China.
Officially, the agenda will focus on the global economy and security.
"The policy of the G7 is clear," EU President Donald Tusk said ahead of the meeting at Ise-Shima. "Any maritime or territorial claim should be based on the international law and any possible dispute should be resolved by peaceful means," he said. "Unilateral actions and the use of force or coercion will not be accepted."
US President Barack Obama this week announced the lifting of a decades-long US arms embargo on Vietnam, making it easier for Vietnam to import US weapons including maritime capabilities.
Obama was applauded by the Vietnamese audience in Hanoi Tuesday when he said "big nations should not bully smaller ones," in apparent reference to the South China Sea dispute.