HAIKOU, April 19 -- China and Vietnam began their 11th joint fishery patrol in the Beibu Gulf on Tuesday.

Two marine police vessels from China and two from Vietnam will observe fishing vessels and make occasional inspections in the common fishing ground in the gulf for five days ending on Saturday.

This year's patrol has been extended from three days, and the traditional one-way route from coast to coast has been modified into a return trip.

The annual joint patrol was launched in 2006 under the framework of the China-Vietnam Beibu Gulf Fishery Cooperation Committee.

The Beibu Gulf is surrounded by land on three sides. It is sandwiched between southern China and northern Vietnam.

The joint sea patrol aims at preserving and developing a stable and friendly atmosphere for fishing.

It has also led to deeper trust between marine law enforcers and strengthened the relationship between the two countries, said an officer from the China Coast Guard.