REUTERS/Kyodo
The vessels entered the 12-nautical-mile territorial waters at about 9:00 am (0000 GMT) off one of the Senkaku islands, which China also claims and calls the Diaoyus, the Japan Coast Guard said.
This is the first time that Chinese Coast Guard ships were spotted sailing through the waters after Beijing raised regional tensions with its declaration of the air zone on November 23.
Chinese vessels have sailed in and out of the contiguous waters around the islands but stayed away from entering their territorial waters since November 22, a Japanese coast guard official said.
Japan's conservative Prime Minister Shinzo Abe has vowed no compromise on sovereignty of the islands and stepped up defence spending, believing that China is trying to change the status quo through growing sea incursions.
Chinese state-owned ships and aircraft have approached the Senkakus on and off to demonstrate Beijing's territorial claims, especially after Japan nationalised some of the islands in September last year.