Philippines asks China to explain 'water cannon' incident

Aquino said the foreign department had been asked to file a "diplomatic message", a day after the Philippines' military chief told reporters of the incident at Scarborough Shoal -- the subject of a bitter territorial row in the South China Sea.

"The first step would be a diplomatic message... directed at the People's Republic of China to ask them to explain what this incident was all about, what their intentions are," Aquino told reporters, when asked whether a formal protest would be lodged.

Scarborough Shoal is a rocky outcrop, considered a traditional fishing ground by Filipinos, which lies just 220 kilometres (135 miles) off the main Philippine island of Luzon. It is about 650 kilometres from Hainan island, the nearest major Chinese land mass.

The South China Sea is one of the world's most important waterways, home to vital shipping lanes and believed to sit atop lucrative mineral deposits.

Both sides engaged in a tense standoff in the area in April 2012, which ended with the Philippines retreating from the shoal.

Aquino acknowledged that Philippine security officials were "not sure at this point in time" whether spraying water cannon at Filipino fishermen was a standard operating procedure by Chinese vessels in the area.

"We don't want to react to a one-off incident," Aquino said.

Aquino said that as of Monday there were Filipino fishermen at the shoal "who were not being harassed or intimidated by any entity".

Philippine armed forces chief General Emmanuel Bautista said the incident occurred on January 27, although he did not divulge further details and it was not clear whether any Filipinos were hurt.

China on Monday refused to directly respond to the allegations, insisting only that it had "indisputable sovereignty" over the area.

China claims most of the South China Sea on historical grounds, including waters near the coasts of its neighbours.

The Philippines, along with Brunei, Malaysia, Taiwan and Vietnam also have competing claims to parts of the sea, and the rivalries have been a source of tension for decades.