After four armed Chinese coastguard warships entered waters that Tokyo claims as its own, Japan protested Beijing on Friday.

Four Chinese vessels carrying what looked like cannons entered Japanese territorial seas in the East China Sea around the disputed islands, which Beijing refers to as the Diaoyu and Tokyo calls the Senkaku, for the first time, according to the Japanese government.

Chief Cabinet Secretary Yoshimasa Hayashi said during a press briefing, "I am not in a position to state what the Chinese side's intentions are, but the intrusion of vessels belonging to China's coastguard into (our) territory is a breach of international law."

China's coastguard said that it had patrolled the waters with vessels carrying weapons.

It said its patrol was a "routine action" to safeguard sovereignty, security and maritime rights, and a "necessary step" for peace and stability as well as to counter Japan's recent "negative moves".

"We advise the Japanese side to be prudent in its words and actions, to reflect on itself and to stop provocations," China's coast guard said, adding that it would step up what it called "law enforcement efforts".

Tokyo lodged a "strong protest" through diplomatic channels calling for a swift exit from the area, Hayashi said. The four vessels stayed in the area for more than an hour and left shortly after midday, he said.

"The intrusion into our territorial waters is extremely regrettable and cannot be tolerated. We will continue to do our utmost to be vigilant and monitor the areas surrounding the Senkaku Islands with a sense of urgency, while dealing calmly and resolutely with China," Hayashi said.

The two countries have repeatedly faced off around the uninhabited Japanese-administered islands.

China's run-ins with the Philippine navy have also been escalating in disputed areas of the South China Sea.