Two China Coast Guard ships briefly entered Japanese waters Friday off Aomori Prefecture, the first Chinese government ships spotted in this area since July 2017, the Japan Coast Guard said.

At around 2:40 a.m. A Japan Coast Guard vessel identified two Chinese ships entering Japan's territorial waters off Cape Tappi in the Tsugaru Strait, which separates Honshu and Hokkaido.

The ships left the waters at around 3:15 a.m. after the Japan Coast Guard warned them via radio, but re-entered Japanese waters off Cape Oma 3½ hours later before eventually exiting the area at around 7:45 a.m.

Under the U.N. Convention on the Law of the Sea, vessels of every country have the right of innocent passage to sail through territorial waters as long as they do not harm the safety of the coastal countries.

Chinese vessels have frequently entered Japanese waters around the disputed Senkaku Islands in the East China Sea. The uninhabited islets are controlled by Japan but claimed by Beijing, which calls them Diaoyu, and Taiwan, which calls them Tiaoyutai.