China and Vietnam have long traded barbs over the strategic and resource-rich South China Sea, which Beijing claims most of.
Tensions have flared in recent months, with Vietnam suspending an oil exploration project operated by Spain's Repsol in an area off its coast claimed by Beijing.
In June, a meeting between top Vietnamese and Chinese generals over border issues was abruptly cancelled, with both sides citing a sudden scheduling conflict.
Hanoi condemned Beijing's latest military drills in the Paracel Islands, a contentious archipelago claimed by both sides.
"Vietnam strongly rejects China's move and seriously requests China to respect Vietnam's sovereignty over the Hoang Sa archipelago," foreign ministry spokeswoman Le Thi Thu Hang said late Tuesday, using the Vietnamese name for the Paracels.
China said last week it was conducting "regular military training in the relevant maritime area located in the northwest of the South China Sea", where the Paracels are located, claiming jurisdiction over the zone.
The two countries fought a brief but bloody skirmish over the Paracels in 1974. More than 70 Vietnamese soldiers were killed and China has had de facto control over the islands since then.
Last week, Vietnam repeated calls for Beijing to halt its activity in the area, and foreign affairs officials in Hanoi met with Chinese embassy staff "to clarify Vietnam's position".
Some $5 trillion in annual shipping trade passes through the South China Sea, which is believed to be rich in oil and gas deposits.
Tensions between Vietnam and China over the sea came to a head in 2014 when Beijing moved an oil rig into waters claims by Hanoi.
The move sparked weeks of deadly anti-China protests across Vietnam.
Taiwan, the Philippines, Brunei and Malaysia also have competing claims in the sea.
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