MANILA - National Security Adviser Hermogenes Esperon Jr. on Wednesday said it is "very hard" to protect the vast expanse of the West Philippine Sea and that government is procuring new technology to improve maritime security.

This after the reported return of Chinese clam harvesting fleets in the disputed sea, which Malacañang has ordered the military to verify.

• LOOK: New images show China's 'most destructive boats' back in West Philippine Sea

Esperon said he was "surprised" to hear that the Chinese ships were back in the area.

"Diplomatic actions could be taken, some military solutions could be taken sa range ng options natin na pwede nating gamitin but it's pretty much on diplomatic action," he said.

When asked how hard it was to protect the area, Esperon answered: "Very hard. West Philippine Sea has 2,000 nautical miles."

"Di pwedeng ang deployment mo diyan ay barko sa barko or fishing boat sa fishing boat. It should be other means, satellite."

Esperon admitted that the Philippines is lacking on surveillance in the West Philippine Sea.

The Philippines will get a new imagery satellite in July but more will be needed to cover the area, he said.

"Because of the size, it becomes a challenge because it's simply too big for our assets to cover but there are enhancements to that," he said in an Oceana Philippines forum on improving transparency in fisheries.

"Sometime July or so, meron na tayong sariling imagery satellite which was a project of the DOST that could give us images of the area and therefore give us a constant picture of the whole domain."

Hermogenes said authorities will intercept illegal fishing vessels spotted in the West Philippine Sea.

"We have the capability, we have monitoring stations sa coastlines natin," he said.

"Now if you would ask me, kumukuha ba sila ng permiso, kalimitan hindi because kulang pa yung enforcement natin eh. So dapat ang focus natin is to develop our surveillance and regulatory capabilities diyan sa lugar na yan so that we could develop it into a rich and viable source of income."

Last month, Filipino fishermen reported that Chinese fishermen were mass harvesting giant clams in the Scarborough Shoal.

• EXCLUSIVE: Chinese harvesting giant clams in Scarborough Shoal

Foreign Affairs Secretary Teodoro Locsin Jr. had said the Philippines has filed a diplomatic note and "will be taking legal action" against China over the incident.

• Philippines to take 'legal action' vs Chinese extraction of Scarborough clams

The Philippines and China have long been involved in a maritime dispute, with Beijing refusing to recognize the arbitral ruling that invalidated its economic claim to around 90 percent of resource-rich South China Sea.