Japan's defence minister has vowed to defend the country's territory after three Chinese government ships entered disputed waters off Tokyo-controlled islands in the East China Sea.
The Chinese coastguard vessels sailed at about 8:30am local time on Sunday (23:30 GMT on Saturday) into territorial waters off one of the Senkaku islands, which China also claims and calls the Diaoyus, Japan's coastguard said.
We can never overlook repeated incursions into territorial waters.
The ships left less than two hours later.
"We can never overlook repeated incursions into territorial waters," Japanese Defence Minister Itsunori Onodera told reporters.
"We need to make diplomatic efforts on one hand. We also want to firmly defend our country's territorial sea and land with the self-defence forces cooperating with the coastguard," he said.
Chinese state-owned ships and aircraft approach the disputed islands from time to time in an effort to demonstrate Beijing's territorial claims, especially after Japan nationalised some of the islands in September 2012.
Sunday marked the first time Chinese ships were spotted there since December 29, when three coastguard ships entered the zone and stayed for about three hours, Japanese officials said.
Japanese coastguard patrol boats have tried to chase Chinese vessels away, fuelling tensions that some fear could spiral into an armed clash. Japan's conservative Prime Minister Shinzo Abe has vowed no compromise on the sovereignty of the islands and recently announced a boost in military spending.
Tensions were heightened in recent months after Beijing announced an air defence identification zone covering a large swathe of the East China Sea, including the disputed islands.