The Haiyang Dizhi 8 and at least two escorts left Vietnam's EEZ and sped towards China Thursday, Reuters reported, citing data from Marine Traffic, a website that tracks vessels.
The survey vessels and escorts had returned to Vietnamese waters on August 13, after having occupied Vietnamese sea territory for about a month earlier.
Vietnam has multiple times demanded that the vessel and its escorts leave Vietnamese waters, condemning their presence as a violation of its sovereignty.
"As Vietnam looks at the issue, Chinese oil survey vessel Haiyang Dizhi 8 and its escorts have continued seriously violating Vietnam's sovereignty and jurisdiction rights in its exclusive economic zone and continental shelf," Foreign Ministry spokeswoman Le Thi Thu Hang had said at a news briefing last month.
Vietnamese President and Communist Party chief Nguyen Phu Trong called last week for restraint in the South China Sea, saying Vietnam would "never compromise" on its sovereignty and territorial integrity.
He also said the Party Central Committee has to foresee what could happen in the coming time in the East Sea to get the nation "prepared for possible opportunities and challenges."
The Haiyang Dizhi 8 had started its scientific survey in early July, said Chinese Foreign Ministry spokeswoman Hua Chunying.
"According to our understanding the work is presently complete," she told a daily news briefing in Beijing, Reuters reported.
The vice chairman of China's Central Military Commission, Xu Qiliang, called for dialogue this week at a meeting with Vietnam's Defense Minister Ngo Xuan Lich in Beijing to address the complex global and regional situation, the Vietnamese News Agency reported Wednesday.
It quoted Lich as saying joint efforts by all countries could help cope with common security challenges.
China illegally claims almost the entire South China Sea, including waters close to Taiwan and Southeast Asian countries Brunei, Malaysia, the Philippines and Vietnam.