Japanese Prime Minister Shinzo Abe on Friday said he would defend disputed islets in the East China Sea at a time when Chinese planes and vessels are frequently present around the area.
The Japanese-administered Senkaku Islands are also claimed by China and Taiwan, where they are called the Diaoyu and the Tiaoyutai, respectively.
"I remain firm in protecting our waters and territories," the premier told a news conference.
"There is no room for negotiation" on the territorial issue, he said.
On Friday, a Chinese Oceanic Administration aeroplane was spotted near Japan's airspace over the islands around noon (0300 GMT), Jiji Press reported, citing Defence Ministry officials.
That prompted Japan's military to scramble F-15 jets, but the Chinese plane left without entering Japan's airspace, the ministry said.
On Thursday, several Chinese fighter jets were also approaching the airspace. The Japanese military sent F-15 jets to the area, but the Chinese jets soon flew out of the area.
In mid-December, Japan scrambled F-15 jets to the area after a Chinese Oceanic Administration aeroplane intruded into the airspace.
Japan's coast guard is to establish a team of several hundred officers to focus on protecting waters around the disputed islets due to the frequent presence of Chinese ships in and around the territorial waters, Kyodo reported, citing unnamed sources close to the matter.
The team, which will be based on the southern island of Okinawa, is to be equipped with more than 10 patrol boats to provide greater security around the islands from April 2015, Kyodo said.