China is already claiming airspace above the artificial islands it is building in the South China Sea, the Philippine military said.
At a Senate hearing yesterday, Vice-Admiral Alexander Lopez, head of the military's Western Command, said Philippine air force and navy planes have been told by radio at least six times to leave a China-held "military security area".
These incidents occurred in the past three months, a senior air force official told Reuters.
China could be testing the waters to see if it can enforce an air exclusion zone above the Spratly Islands chain in the South China Sea, the official said.
China replied that it has no intention to do so. In a news briefing yesterday, China's Foreign Ministry spokesman Hua Chunying said that while China had the sovereign right to declare an air exclusion zone to assure airspace safety, "the current situation in the South China Sea is peaceful and stable".
Taking a swipe at the Philippines, she said: "For another party to stir up the issue, that China might want to set up an air exclusion zone over the South China Sea, evidently there are ulterior motives."
Vice-Admiral Lopez was not asked for details during the Senate hearing, but one incident was reported two weeks ago, when a Chinese frigate stationed near a reclaimed reef challenged a Philippine aircraft on a routine reconnaissance patrol. The incident occurred on April 19.
The warship flashed lights and radioed the plane to leave the area, military spokesman Lieutenant-Colonel Harold Cabunoc said on April 24.
China disputed this account.
China's Foreign Ministry said the Chinese ship did not flash lights at the plane, but it did radio the pilot because of "multiple intrusions into the area above waters near China's islands and reefs over recent days". The plane was reportedly flying 1,500m over Subi Reef, where China is said to be planning a 3km airstrip.
The latest satellite images showed that China has already reclaimed enough land to build at least two airstrips, harbours and buildings the size of large shopping malls in all seven reefs it occupies in the island chain.
China claims most of the potentially energy-rich South China Sea. Vietnam, the Philippines, Brunei, Malaysia and Taiwan have competing claims.
Admiral Samuel Locklear, the US' most senior military commander for Asia, has warned that China could install long-range detection radars, base warships and warplanes on its islands, potentially giving it the ability to enforce an air defence identification zone.
At yesterday's Senate hearing, National Security Adviser Cesar Garcia said disputes in the South China Sea "has in fact overtaken all security issues in our hierarchy of national security concerns".
General Gregorio Catapang, the Philippine military chief, told senators that Congress should increase spending to modernise the military.
"We don't have the luxury of time. The threats are already there," he said.
Separately, Cambodia threw its support yesterday behind China's position on settling South China Sea disputes, arguing that territorial conflicts should be tackled between claimants and not involve ASEAN.
With additional reporting by Teo Cheng Wee in Beijing
This article was first published on May 8, 2015.
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