This handout picture taken by the Japanese Coast Guard on Nov. 2 shows a Chinese Coast Guard ship cruising in the East China Sea near the disputed islets known as the Senkaku islands in Japan and the Diaoyu islands in China. China declared an air defense identification zone that included the disputed islands on Saturday. (AFP/Getty Images)

China said Saturday that noncommercial aircraft entering a broad zone over the East China Sea must first identify themselves to Beijing, at the risk of facing “defensive emergency measures” by Chinese armed forces.

China’s establishment of a so-called air defense identification zone, announced by its Ministry of National Defense, adds a new dimension to the simmering territorial dispute with Japan and raises the odds of armed conflict.

The eight uninhabited islands at the center of that dispute fall within China’s new aerial zone. Based on guidelines that China’s Defense Ministry released Saturday, any Japanese aircraft flying around those islands would need to submit their flight plans to China’s Foreign Ministry or civil aviation administration. They would also need to maintain radio communication with Chinese authorities.

China did not detail what measures it would take against aircraft that disobey the new rules, but defense experts say its military could scramble jets or even shoot down planes it views as a threat.

Later Saturday, the country’s air force conducted its first air patrol after the establishment of the new zone, with two large scouts leading the mission and early-warning aircraft and fighters providing support and cover, according to the official Xinhua News Agency.

“The patrol is in line with international common practices, and normal international flights will not be affected,” said Shen Jinke, spokesman for the air force. He said the Chinese armed forces would take measures to deal with any air threats to protect the security of the country’s airspace.

Numerous countries, including the United States and Japan, have air defense identification zones of their own. The zones are established to help countries track or monitor aircraft nearing their territories, but in this case, the zones of Japan and China overlap. Security experts worry that China’s new zone could increase the likelihood of a mishap that sparks a wider armed conflict, drawing in the United States, which is treaty-bound to protect Japan.

China’s move makes “the already dangerous area surrounding the [disputed] islands even more ripe for an inadvertent collision,” said Paul Haenle, director of the Carnegie-Tsinghua Center for Global Policy at Tsinghua University in Beijing.

In a statement, the Japanese Foreign Ministry said, “The airspace the Chinese side established today is totally unacceptable and extremely regrettable as it includes the Japanese territorial airspace over the Senkaku Islands, an inherent territory of Japan.

“Unilaterally establishing such airspace and restricting flights in the area is extremely dangerous as it may lead to miscalculation in the area,” the statement said.

U.S. Secretary of Defense Chuck Hagel expressed strong concern over the Chinese decision. “We view this development as a destabilizing attempt to alter the status quo in the region. This unilateral action increases the risk of misunderstanding and miscalculations,” Hagel said in a statement Saturday. “This announcment by the People’s Republic of China will not in any way change how the United States conducts military operations in the region.”

A Chinese Defense Ministry spokesman, Yang Yujun, said China had created its zone “with the aim of safeguarding state sovereignty, territorial land and air security,” according to a transcript on the ministry’s Web site.

The aerial zone does not cover the South China Sea, where China is engaged in several other territorial disputes, notably with the Philippines and Vietnam. But Yang said China will establish additional zones “at the right moment after necessary preparations are completed.”

The struggle between China and Japan over control of several tiny land masses in the East China Sea escalated last summer, when Tokyo purchased three of the islets from a private landowner. Since then, the neighbors have been locked into a cat-and-mouse game around the islands, with both sides sending ships to ward off the other.

But increasingly, the confrontation is happening above the waters, not just in them. Both sides have recently scrambled fighter jets, and two months ago Japan’s government said an unidentified drone flew near the islands, the first such incident of its kind.

Although leaders on both sides have talked about wanting to repair badly frayed ties, little progress has been made. Japanese Prime Minister Shinzo Abe says that the islands are an “inherent” part of Japanese territory and that the validity of its claims aren’t up for debate. Japan has increased its military spending, with plans to beef up its forces around its perimeter islands. Chinese defense experts, meantime, say the country finally has the military power to make a play for contested territory that China controlled centuries ago.

“If China is to implement fully the policy of its air defense identification zone, there will be an increasing likelihood of conflict and confrontation in the air” between Japan and China, said Zhou Yongsheng, a specialist in Sino-Japanese issues at the University of International Relations in Beijing. “But I think China shouldn’t be afraid of conflicts, because we’ve been suppressed by Japan for so many years. We should safeguard our sovereign interest.”

Simon Denyer, Liu Liu and Guo Chen in Beijing contributed to this report.