BEIJING — The action in the skies over the East China Sea started simply enough.

Last week, the Chinese government sent a civilian surveillance plane, a twin propeller aircraft, to fly near the uninhabited islands at the heart of a growing feud between China and Japan. Tokyo, in response, ordered F-15 fighter jets to take a look at what it considered Chinese meddling. The Chinese then sent their own fighters.

It was the first time that supersonic Chinese and Japanese military fighters were in the air together since the dispute over the islands erupted last year, significantly increasing the risk of a mistake that could lead to armed conflict at a time when both countries, despite their mutual economic interests, are going through a period of heightened nationalism that recalls their longstanding regional rivalry.

The escalation comes amid a blast of belligerent discourse in China and as the Obama administration has delayed a visit to Washington requested by Shinzo Abe, the new prime minister of Japan, the United States’ main ally in Asia. After the rebuff, Mr. Abe announced that he would embark on a tour of Southeast Asia intended to counter China’s influence in the region. On Friday, as Mr. Abe cut short his trip to return to Tokyo to deal with the hostage crisis in Algeria, Secretary of State Hillary Rodham Clinton said in Washington that Mr. Abe would meet with President Obama in the second half of February.

For Japan and China, what began as a seemingly minor dispute is quickly turning into a gathering storm, military analysts and Western diplomatic officials warn, as each country appears determined to force the other to give ground.