Colonel Duong De Dung, the commander of Da Nang Border Guard, said at a conference that Chinese fishing boats illegally entered Vietnamese territory to fish, and usually in groups of 25-32.
They were accompanied by armed vessels and transport ships when they came deep into Vietnamese territory.
The Da Nang border guard said they usually reached the scene as soon as they detected the boats and ordered the Chinese fishermen to leave immediately.
In most cases, the order was obeyed, it said.
The Chinese boats usually entered Vietnamese waters during bad weather when there were no border guard patrols, it added.