REPORTS that a Chinese warship fired a warning shot at a Filipino fishing vessel near Mischief Reef on Thursday is unverified, the Department of Foreign Affairs (DFA) said on Friday.

"That's unverified," Foreign Affairs spokesperson Charles Jose said in a text message when asked about the alleged incident.

Palawan-based boat operator Pasi Abdulfatah said the incident involves one of the boats he owns. He said the incident occurred near Mabini Reef (Johnson South Reef), which is also near the Mischief Reef, one of the areas being claimed by China, Philippines, Vietnam and Taiwan.

Abdulfatah said his boat was fishing near the reef when a Chinese vessel fired the warning shot. He said the scared fishermen left the area and transferred near an area occupied by Vietnam.

The boat operator said they did not report the incident to the military or to coast guard because they are used to harassments by China.

Admiral Alexander Lopez, commander of the military's Western Command, said they are not aware of the incident, and therefore could not make any comment.

"We have no report so far, no basis to react," said Lopez.

Defense Secretary Voltaire Gazmin echoed Lopez and expressed concern over the incident.

"We have not received any report yet but if indeed this happened, it is a cause of grave concern," said Gazmin in a text message to the media.

China has been building aggressively on the Mischief Reef since January 2015, and in a matter of weeks has dredged sand and rocks to the reef to form an artificial island that can house actual government facilities.

Mischief Reef is not the only site of China's massive reclamation projects in a region now seen with the potential military flashpoint in the future.

About 200 miles from Mischief Reef is the Fiery Cross Reef, where China has built a docking harbor and a military-sized airstrip.

Reports of intimidation between China and Filipino vessels were not new. China has been warning air and sea vessels away from Mischief and Fiery Cross Reefs in the past months, referring to the contested features as Chinese military areas.

The Philippines and China have a protracted territorial dispute on resource-rich West Philippine Sea, but it wasn't until 2011 during the naval standoff at the Scarborough Shoal that tensions began piling.

Manila filed a diplomatic protest before a United Nations-backed court in January 2012, but China refused to participate.

Since then, Beijing's campaign had been to open bilateral talks with claimants while aggressively changing the features in one of the world's most important sea lane.

Most of the international community, led by the United States, raised concerns on the peace and stability of the region where more than $5 trillion of sea-borne trade passed by annually. (CVB/VR/Sunnex)