Ship tracking data revealed Beijing deployed a controversial survey vessel with a Coast Guard escort on Tuesday as the row in the disputed waters heats up. China often deploys the controversial spy vessels into waters claimed by other nations in the South China Sea to monitor rivals, as well as for military purposes.
It is an action which is interpreted as an assertion of its claim to “historic rights” over nearly all of the disputed waterway.
It comes as the new prime minister of Japan Yoshihide Suga prepares to visit Vietnam next week, a country which Beijing views as a strategic rival.
It is expected that Japan could be planning to sell defence equipment to the one-party state.
The shipping data reviewed by RFA revealed the Shiyan-1 survey and research ship departed Haikou Bay, in China’s Hainan province, on Monday.
It then came within 70 nautical miles of Vietnam’s Quang Ngai province on Tuesday and as of Wednesday morning, the vessel was 78 nautical miles off the coast of Binh Dinh province on Vietnam’s central coast.
The actions prompted Hanoi to send five ships operated by Vietnam’s maritime law enforcement agency to monitor both the vessels as they travelled into the country’s waters.
Ahead of Japan’s visit to Vietnam, Mr Suga, who replaced Shino Abe last month, called his Vietnamese counterpart Nguyen Xuan Phuc.
Kato Katsunobu, Chief Cabinet Secretary of Japan, said of the call: “Japan will work with various nations to realize a free and open Indo-Pacific region. That’s the idea we have.”
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Brunei, Malaysia, Vietnam and Taiwan also have claims.
The nation uses a U-shaped “nine-dash line” on its maps marks a vast expanse of the waters that it claims.
This includes large parts of Vietnam’s continental shelf where it has awarded oil concessions.