The vessels sailed into the 12-nautical-mile band around the Tokyo-controlled Senkaku islands -- which Beijing calls the Diaoyus -- at around 0030 GMT, the Japanese coastguard said.
The incursion came a day after Japan's defence minister said Tokyo could be a key participant if conflict breaks out in Asia as he warned China was seeking to exploit difficulties between allies.
It was the latest in a series of forays by Chinese ships in a year-long spat between Tokyo and Beijing that has sent relations plummeting.