Japan and China on Wednesday signed a document to start operating a bilateral communication mechanism aimed at averting unintended military clashes, sidestepping a long-running territorial row over a group of small islands in the East China Sea.

Under a memorandum signed by the two countries following talks between their leaders in Tokyo the same day, the mechanism includes a hotline and regular dialogue between senior Japanese and Chinese defense officials, according to the Japanese Defense Ministry.

But uncertainty hangs over whether the move will help ease tensions linked to China's claim over the Japanese-controlled Senkaku islets in the East China Sea. The mechanism will be put into practice without any reference to its geographical coverage, it said.

The plan to set up the "Maritime and Aerial Communication Mechanism" was first agreed between the two countries in 2007.

But it took more than a decade to wrap up the negotiations, due in part to Tokyo's decision to put the Senkaku Islands under state control in 2012, drawing sharp opposition from Beijing, which calls the islands Diaoyu. Chinese government vessels have since entered Japanese territorial waters near the islets on numerous occasions.

According to Japanese government sources, Japan has insisted that the waters and airspace around the Senkaku Islands should not be covered by the bilateral communication mechanism, based on its idea that the islets are an inherent part of Japanese territory.

But China has argued otherwise and the two sides have ended up agreeing not to make any specific geographic references over the operation of the mechanism.

The mechanism will start operating from June 8, the 30th day after the signing of the memorandum. Technical arrangements are underway for the hotline, which is expected to connect senior Japanese and Chinese defense officials, and it will open "at the earliest possible date," the Japanese Defense Ministry said.

A meeting at director-general level and another meeting at a lower level will be held annually to look into the operation of the system and technical problems that need to be improved.

Written notification is needed if either country decides to suspend or terminate the system, according to the ministry.