The aircraft were observed by the Vietnamese Fisheries Surveillance Force. The official Vietnam News Agency said its reporters on board surveillance vessels observed the aircraft as well as two Chinese minesweepers patrolling the region.
The report said China has more than 100 vessels, including five military ships, stationed around the rig. Vietnamese boats were prevented from entering traditional fishing grounds and the report said Chinese Coast Guard vessels came within 65 feet of Vietnam's.
Both sides met in Hanoi this week in an effort to resolve tensions that erupted when China deployed an oil drilling rig to the contested waters in early May. Both sides say they have a legitimate right to the maritime territory.
China described the situation through its official Xinhua News Agency as complicated, but said both sides could work together to find a political and diplomatic solution to the issue.
Hanoi, for its part, said the need for a resolution was urgent. Both sides, the government said, could find a way to work together under the terms of international maritime law.