A Chinese state-owned aircraft has flown over islands at the centre of a dispute between Japan and China, the Japanese defence ministry says.
A spokesperson for the ministry confirmed media reports that a fixed wing plane from the Chinese Maritime Surveillance agency was the first that the Japanese military had ever recorded as intruding into its airspace without prior permission.
China's foreign ministry termed Wednesday's surveillance flight "completely normal".
The Japanese airforce scrambled eight F-15 fighter jets and an E-2C early warning aircraft to respond to the perceived threat, the defence ministry said.
The Chinese plane intruded into Japanese airspace at 11:06am local time (02:06 GMT) over the Japanese administered Senkaku Islands in the East China Sea, Chief Cabinet Secretary Osamu Fujimura said.
Tokyo immediately lodged a protest with Beijing over the matter, Fujimura said. The Chinese plane had left the area before the F-15s arrived, he added.
The islands are also claimed by China and Taiwan, where they are known as the Diaoyutai and Tiaoyutai, respectively.
Earlier in the day, four Chinese surveillance ships also entered what Japan called its territorial waters around the islands, the Japan Coast Guard said.
Japan's purchase of four of the islands in September from a private owner set off anti-Japan protests in dozens of Chinese cities and prompted a boycott of Japanese products
The latest incident comes just days before a Japanese election that is expected to return to power the conservative Liberal Democratic Party (LDP), with former prime minister Shinzo Abe at the helm.
Abe has vowed to take a stern stance in the dispute over the islands, which are near potentially huge maritime gas reserves, and has said that the ruling Democratic Party's mishandling of its diplomacy had emboldened China.
Nanjing massacre remembered
The latest dispute comes as China marked 75 years since Japanese troops embarked on a campaign of mass killing and rape in the city of Nanjing.
Nearly 10,000 people sang the Chinese national anthem at a commemoration at the Nanjing Massacre Museum, as soldiers in dress uniforms carried memorial wreaths across a stage and officials urged remembrance of the past.
"We are here to recall history, grieve for compatriots who suffered and died, and educate the people... about the lessons of history," said Nanjing Communist Party chief Yang Weize, the only government official who spoke.
China says 300,000 civilians and soldiers died in a spree of killing, rape and destruction in the six weeks after the Japanese military entered its then capital on December 13, 1937.
Some foreign academics put the number of deaths lower, including China historian Jonathan Spence who estimates that 42,000 soldiers and citizens were killed and 20,000 women raped, many of whom later died.