Beijing has expressed concern about Vietnam's plan to equip fishery patrol boats with "military-use weapons".

Yi Xianliang, deputy director-general of the Department of Boundary and Ocean Affairs under the Foreign Ministry, raised the issue after the Vietnamese government amended weapon-related laws and regulations on July 29.

As a result, the country's fishery administration ships "will be equipped with military-use weapons as of Sept 15", Vietnam local media Tuoi Tre Online reported on Friday.

The fishery watchdog personnel and sailors will be allowed to use pistols and machine guns, the news reports said.

Experts said coast guard ships are generally allowed to be equipped with arms, but fishery patrol boats are not.

Yi said he noticed the report and said Vietnam's choice is "unwise within the current context".

"We firmly oppose practices that make the use of force a primary means of law enforcement," Yi said.

The senior diplomat said Hanoi is expected to "realize the seriousness of the issue".

Vietnam has reacted belligerently and heightened tensions in the region since China's oil drilling operations near Zhongjian Island of China's Xisha Islands began on May 2.

By June 13, Vietnamese vessels had rammed Chinese ships 1,547 times. The attacks came even though Hanoi recognized China's sovereignty over the islands in official statements and even in high school textbooks 40 years ago.

As Hanoi continues to flex its maritime muscle, Japan and Vietnam signed a deal on Friday in which Tokyo will provide Hanoi with six used vessels for a total $5 million.

The Associated Press said the six vessels are "part of a grant aid package that will boost Hanoi's maritime security patrol capacity at a time the country is locked in a territorial standoff with China in the South China Sea".