The Philippine defense secretary says an anchored Filipino fishing boat has sunk in the disputed South China Sea after being hit by a suspected Chinese vessel which then abandoned the 22 Filipino crewmen.

Defense Secretary Delfin Lorenzana on Wednesday called for an investigation of the June 9 sinking at Reed Bank and asked that diplomatic steps be taken to prevent a repeat of the incident. It's a delicate development in the long-contested waters.

The Philippine coast guard says it is checking whether Chinese fishermen were involved or those from other neighboring countries and if the collision was intentional.

Lorenzana says the 22 Filipino crewmen of the sunken F/B Gimver 1 were rescued by a Vietnamese vessel.