Japan said on Sunday that four Chinese vessels sailed into territorial waters around disputed islands in the East China Sea while Tokyo tried to engage with Beijing to press North Korea over the latest nuclear test.
The Japan Coast Guard said the four coastguard vessels sailed around 10:30 am into waters surrounding the islands, administered as Senkaku by Japan and claimed as Diaoyu by China. But they left about 90 minutes later.
This incident comes at a time of heightened tension in the region after Pyongyang conducted its fifth and most powerful nuclear test on Friday.
Japan, South Korea and the United States have asked China to use its leverage to persuade Pyongyang to comply with UN sanction resolutions as China is one of North Korea's few allies.
Japan has repeatedly complained about the increasing number of Chinese ships to the island chain that has escalated the regional tensions.
But, Sunday was the first time when the Chinese ships had sailed into the waters after Japanese Prime Minister Shinzo Abe met Chinese President Xi Jinping at the G20 Summit in Hangzhou, China, last week.
At the summit, Xi told Abe to "put aside disruptions" and sought to improve ties. However, with the Chinese leader also urged Japan to "exercise caution" on territorial disputes.
The conflict between Japan and China has been rising due to "China's incursions into the waters of the Tokyo-controlled disputed islands". Since August 5, Japan has lodged at least 32 protests regarding 30 intrusions by Chinese vessels in the territorial waters.
China regards them as its own, rejecting the view it violates Japan's territorial waters.
Japan working towards boosting defence ties with the Philippines and other Southeast Asian nations, some of which have their own disputes with Beijing in the South China Sea.