MANILA - Malacañang on Tuesday defended the government’s decision to allow China to explore Benham Rise, saying conducting such research is an expensive endeavor.

The Department of Foreign Affairs (DFA) earlier granted the request of the Chinese Academy of Sciences’ Institute of Oceanology to do research at the Benham Rise, a resource-rich underwater plateau located east of Isabela.

Critics blasted the move, saying it could undermine Manila’s interests in the waters, which the United Nations in 2012 awarded as an extension of the Philippines’ continental shelf.

In a news conference, Roque said China was allowed to do the study since it met the qualifications, one of which is that Filipino researchers must be allowed to join Chinese researchers.

“Only China has qualified so far. There are other applicants. Unfortunately, they did not qualify according to fixed guidelines already set by the government,” he said.

“No one has applied. And no one can do it because, apparently, it’s capital intensive.”

Senator Francis Pangilinan on Monday questioned why China, which has an ongoing dispute with the Philippines over the South China Sea, was chosen to conduct the research despite its maritime conflict with Manila.

“What will the country stand to gain from this marine scientific research? Why do we need to partner with China? Can't the Philippines do it on its own? What is in store for China after the research? How long will this be carried out, and what will be the coverage of the research? What are the mechanisms and guidelines in place in the conduct of the activity?” Pangilinan said in a statement.

“Most importantly, what would be the impact of such joint undertaking on the Philippines' national interest and security?” said the senator, who is president of the opposition Liberal Party.

Pangilinan said he had to raise these questions because “history and experience tell us that China is not exactly the most trustworthy partner for such an activity.”

Meanwhile, former national security adviser Roilo Golez said he was also puzzled why Manila allowed China to conduct the scientific research.

Golez noted that China may be "lusting" after the natural resources in Benham Rise, which is supposedly rich in fish and methane gas hydrates.

• China lusting after Benham Rise resources: Golez

"I’m very worried that China may be lusting for the resources available there plus the geostrategic value...The Constitution is very clear that the state must protect our marine wealth in our exclusive economic zone, territorial sea, etc., and reserve its use exclusively for Filipino citizens," Golez told ANC.

Golez said the Philippines' decision to allow China to survey the area gives Beijing an "opening" that could have "strategic implications" in terms of geopolitics.

"They want to go into the Western Pacific, which is right now dominated by the US, by Japan...That will enable them to do oceanographic studies to find out what is under the sea," he said.

China may also be looking for a "thermocline," a transition layer between deep and surface water "where there's an abrupt change in temperature" that could allow submarines to freely operate.

Pangilinan called on the administration to be transparent in its dealings with China “to allay fears of the people that it is betraying our national sovereignty and patrimony.”

Since assuming power, President Rodrigo Duterte has sought to downplay Manila’s South China Sea dispute with Beijing in pursuit of better economic ties with Asia’s largest economy.

• Duterte, China's Xi agree not to 'waste lives' over sea dispute