China is once again facing off against its smaller and weaker neighbors who all lay claim to a string of islands, coral reefs and lagoons in the South China Sea.
The Philippines says China warned its air force and navy planes at least six times to leave areas around the disputed South China Sea last month.
Philippine military commander, Vice Admiral Alexander Lopez, told a Senate hearing that Beijing "appears to be in effect imposing an air defense zone over the disputed area."
"As we were conducting routine maritime air patrols and flying in international airspace, our air force aircraft were challenged over the radio," Lopez said, adding such warnings are dismissed and pilots reply that they are navigating international space.
Chinese Foreign Ministry spokesman Hong Lei said that Philippine planes had "illegally flown over Chinese waters on numerous occasions recently" and that Chinese forces had issued a radio warning.
A series of high-resolution satellite images show that China has intensified the construction of artificial islands in the disputed sea, sometimes doubling or tripling the size of existing features.
The US military claims that China could eventually deploy radar and missile systems on its outposts. China has denied all accusations, saying the work is to improve living conditions for people in the area and help with weather forecasting and search and rescue work.
Meanwhile, Cambodia has thrown its support behind China's position against the Association of Southeast Asian Nations (ASEAN), arguing that territorial conflicts should be tackled between claimants.
After a meeting with diplomats from 28 countries, Foreign Affairs Secretary of State Soeung Rathchavy told reporters that "ASEAN can't settle this dispute. We are not a legal institution, it's the court that settles who's right and wrong."
China provides huge economic and military support to Cambodia, its closest ally in Southeast Asia.
China claims 90 percent of the strategic waters and has long said ASEAN is not a party to the dispute. Vietnam, the Philippines, Brunei and Malaysia have competing claims.
Chinese reclamation work in the South China Sea dominated discussions in ASEAN's latest summit in Malaysia last week, which issued a statement saying such activity had "eroded trust and confidence." China responded by saying it was "severely concerned" over the statement.