UPDATE included on November 24
[English text has been added to the Chinese map for clarification.]
Telegram from New China (XINHUA) Network in Beijing on November 23:
The government of the People's Republic of China, while referring to the "National Defence Law of the People's Republic of China" from March 14, 1997, the "Civil Aviation Law of the People's Republic of China" from October 30, 1995, and the "Basic Regulations for Air Traffic of the People's Republic of China" from July 27, 2001, announces the delimitation and setting up of a distinguished air defence zone in the East [China] Sea.
[Official announcement by XINHUA 新华 news agency on November 23, 2013]
Later that day, the BBC World Service quoted XINHUA on their website. Here an excerpt from the BBC report:
China has demarcated an "air-defence identification zone" over an area of the East China Sea, covering islands that are also claimed by Japan.
China's defence ministry said aircraft entering the zone must obey its rules or face "emergency defensive measures".
The islands, known as Senkaku in Japan and Diaoyu in China, are a source of rising tension between the countries.
Japan lodged a strong protest over what it said was an "escalation".
"Setting up such airspace unilaterally escalates the situations surrounding Senkaku islands and has danger of leading to an unexpected situation," Japan's foreign ministry said in a statement.
Taiwan, which also claims the Diaoyu/Senkaku islands, expressed regret at the move and promised that the military would take measure to protect national security.
In its statement, the Chinese defence ministry said aircraft must report a flight plan, "maintain two-way radio communications", and "respond in a timely and accurate manner" to identification inquiries.
"China's armed forces will adopt defensive emergency measures to respond to aircraft that do not co-operate in the identification or refuse to follow the instructions," said the statement.
It said the zone came into effect from 10:00 local time (02:00GMT) on Saturday.
[Source: BBC World Service on November 23, 2013]
A Global Network report, based on [today's] TV report by Japan's NHK channel, is saying:
An aircraft on patrol for Japan's aviation self-defence group confirmed that, on the same day of [November] 23, two Chinese military planes entered the East [China] Sea area in succession while being on patrol. One of these military planes was nearing the air space of the [Senkaku / Diaoyu] islands at a distance of up to 60 km from the North but did not enter [the island's] territorial air space. Japan's aviation self-defence dispatched combat planes in an emergency take-off to engage in pursuit and observation.
According to Japanese defence officials, the Chinese planes were identified as air force reconnaissance planes belonging to the Shaanxi Y-8 and Tupolev TU-154 type.
It was the Tu-154 that came near to the Senkaku / Diaoyu islands.
[Source: news.163 quoting the Global Times 环球时报, Beijing, on November 24, 2013]
According to another article originating from Reuters news agency and dating from November 23, vessels from the China Maritime Surveillance and the Japanese Coast Guard were already seen at small distance near the disputed islands, called Senkaku in Japan and Diaoyu in China, on November 10, 2013.