ISHIGAKI, Japan >> When the flotilla of 21 fishing boats arrived at an island chain at the center of a growing territorial dispute with China, the captains warned the dozens of activists and politicians aboard not to attempt a landing.

Ten of the activists jumped into the shark-infested waters anyway, swimming ashore on Sunday and planting the rising sun flag that evokes painful memories of Imperial Japan’s 20th-century march across Asia.

“We feel that they dragged us into an international incident,” said Masanori Tamashiro, the captain of one of the boats that made the eight-hour voyage to the uninhabited outcroppings northwest of here called the Senkakus in Japan and the Diaoyu in China.

That feeling is widely shared in Japan, where a small band of nationalists has pushed the country to assert itself more boldly to counter China and South Korea’s explosive economic rise and China’s quickly evolving territorial ambitions.

The nationalists have gained traction for their cause in recent months by taking advantage of the government’s political weakness, forcing the governing party to take a tougher stand on the Senkakus.

But the activists are also tapping into a widespread anxiety over China, and the resulting acrimony over the Senkakus has already become a potential international flash point, raising the specter that the United States, Japan’s longtime defender, could be pulled into the conflict.

Japanese fears intensified two years ago during the last major flare-up over the Senkakus, when China retaliated for Japan’s arrest of a fishing captain by starving Japan of the rare earths needed for its already struggling electronics industry. That anxiety became more pronounced in recent months as China expanded its claims in the nearby South China Sea, challenging Vietnam, the Philippines and others over more than 40 islands in a vast area, and backing its statements with aggressive moves that included sending larger patrol boats to disputed waters.

There is still little appetite in pacifist Japan for a full-blown confrontation with China. But analysts say consensus is growing on the need to stand up to China as power in the region appears to slip further from economically fading Japan and the United States.

“We are all gearing up for an international tug of war in this region,” said Narushige Michishita, an expert on security issues at the National Graduate Institute for Policy Studies in Tokyo. “Whenever the distribution of power changes in a dramatic way, people start to redraw lines.”

That is precisely what is happening in the South China Sea, which has received more international attention than Japan’s territorial battles. But experts say the increasingly shrill war of words between Japan and its East Asian neighbors, including China and South Korea, is potentially more explosive. Unlike in the South China Sea, where the frictions center on competition for natural resources, the East Asian island disputes are more about history, rooted in lingering — and easily ignited — anger over Japan’s brutal dominance of its neighbors decades ago.

Those raw emotions were loosed over the weekend, as hundreds and possibly thousands of Chinese — in protests that were at least tolerated by the government — poured into the streets in several cities to denounce Japan’s claims over the islands.

“The stakes are much higher in East Asia because you have bigger countries in close proximity, and the conflicts are more direct and emotional,” said Kent Calder, director of the Edwin O. Reischauer Center for East Asian Studies at Johns Hopkins University.

The ramifications for the United States are also potentially more troubling, analysts said. The United States has been urging Japan and South Korea to pick up more of the burden of defending against China and North Korea, but the countries’ latest standoff over islets that sit between them, known as Takeshima in Japan and Dokdo in Korean, contributed to South Korea’s decision to back out of an agreement to share military intelligence with Japan.

An even bigger, though remote, risk for the United States, some analysts said, is that it could be dragged into an armed conflict between China and Japan, which it is obligated by treaty to defend.

“There is a real possibility that if diplomacy fails, there will be a war,” said Kazuhiko Togo, a former career Japanese diplomat who has written on the island issues.

The current row between Japan and China was started by Tokyo’s governor, Shintaro Ishihara, a longtime and outspoken advocate of conservative issues. Last spring, he said he wanted Tokyo to buy the islands from their current owner, a Japanese citizen, to better defend them from China. Under pressure not to look weak in advance of elections, Prime Minister Yoshihiko Noda quickly said the central government would buy the islands instead.

That set off a tit-for-tat between activists from both countries. First, seven Hong Kong activists landed last week on Uotori, the largest of the disputed islands and were among 14 Chinese arrested by Japan and quickly deported. Japanese nationalists retaliated with their landing on the same island on Sunday. (In a sign of how small the circle of Japanese activists is, one of the eight national lawmakers who joined the flotilla, Eriko Yamatani of the opposition Liberal Democratic Party, was also part of a recent episode that helped set off the latest battle between South Korea and Japan over their disputed islands.)

That flotilla left from here, on Ishigaki island, on the southern edge of the Okinawa chain that is about 80 miles from the Senkakus.

Yoshiyuki Toita, a 42-year-old member of Ishigaki’s city assembly, was one of the few local residents who joined the expedition.

“Japan has come to the point that it must change,” Toita said. “The era of just depending on the United States is over.”

Even so, Toita agreed with mainstream opinion that Japan should cleave more closely to the United States. Still, the government has taken at least some actions to show its own willingness to push back at China, most notably redrawing its national defense strategy, which had once focused on the Soviet Union in the north, but now will concentrate on protecting against China in the south. And an opinion poll last October conducted by the prime minister’s office showed a growing wariness, with more than 70 percent of Japanese saying they do not have “friendly feelings” toward China.

Such sentiments have even made inroads here in Ishigaki, a part of Okinawa, where a deep pacifism was born of the anger at the Japanese Imperial Army’s forcing of civilians to commit suicide during World War II, as well as the heavy American troop presence after the war.

As Chinese warships and patrol boats have become a more frequent sight in waters near here, some islanders have begun to speak out more in support of the American and Japanese militaries, even as sentiment against United States bases remains strong. Since the events of two years ago when China cut off supplies of rare earths, Ishigaki’s mayor, Yoshitaka Nakayama, began flying the rising sun flag in front of city hall for the first time since World War II.

At the same time, Nakayama, 45, said he values his island’s growing trade and tourism links to the Chinese-speaking world, especially Taiwan, which also stakes a claim to the Senkakus.

Tamashiro, the fishing boat captain, expressed similar conflicted feelings, even as he has begun taking more activists to see the islands.

“Basically, fishermen don’t want the politics to disrupt their livelihoods,” Tamashiro said. But at $4,500 per boat charter, he said, going to the Senkakus “is not bad money.”

© 2012 The New York Times Company