The Chinese vessel, the Haiyang Dizhi 8, was speeding away from Vietnam’s exclusive economic zone towards China on Thursday morning under the escort of at least two other Chinese ships, according to data from Marine Traffic, a website that tracks vessel movements.
China claims almost all the energy-rich waters of the South China Sea but neighbors Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims.
Tension between Hanoi and Beijing escalated when China sent the vessel to conduct seismic surveys in waters off Vietnam in early July.
The foreign ministry in Hanoi has repeatedly accused the vessel and its escorts of violating Vietnam’s sovereignty and has demanded that China remove its ships from the area.
The ministry did not respond immediately to a Reuters email seeking comment on Thursday.
Police broke up a brief protest in August outside the Chinese embassy in Hanoi over the survey vessel.