The arrests come as confrontations between the two Asian neighbours over contested reefs and waters in the strategic South China Sea have escalated in recent months.

Two men were arrested at Manila airport last week after they allegedly conducted surveillance on Filipino navy and other government vessels supplying military garrisons in the disputed Spratly archipelago.

The men, using a drone and high-resolution solar-powered camera, recorded activities at a naval base, a coast guard station, an air base and a dockyard in Palawan province, the closest major lan director Jaime Santiago told a joint news conference.

"We consider them very dangerous to national security because of course, if this falls into other hands, this could be very dangerous for our personnel in the base and also those on board our ships," Philippine military chief General Romeo Brawner told the news conference.

The spies disguised themselves as buyers of marine products or members of legitimate organisations.

Two other Chinese men were separately arrested elsewhere in Manila and another in the central city of Dumaguete last week, Santiago said.

It followed the arrest this month of a Chinese software engineer named Deng Yuanqing and two Filipino associates suspected of spying on military and police camps -- allegations that were dismissed by the Chinese embassy in Manila.

NBI cybercrime unit chief Jeremy Lotoc said a witness told the authorities Deng met with the five detained suspects once a month, acting on instructions from an unnamed "foreign national" in China.

Brawner said it was premature to conclude that the spying was state-sponsored, with Filipino authorities yet to identify the end-receiver of the intelligence gathered.

"This is perhaps just the tip of the iceberg, many can still be caught doing these activities," Brawner said. "There are more of them."

Some of the suspects have been living in the Philippines since 2002 and did not have any criminal records, immigration bureau spokeswoman Dana Sandoval told the news conference.

Security officials paraded the five suspects, handcuffed to each other, before the media along with the confiscated "military-grade" spying equipment.

Beijing claims most of the strategic South China Sea despite an international ruling that its assertion has no legal basis.

The Chinese embassy in Manila did not immediately respond to AFP's request for comment on the fresh arrests.

On Saturday, it described the spying allegations against Deng as "baseless speculation and accusation".

The mission said it asked for its consul to visit the detained man, and urged Manila to "protect the legitimate rights and interests of Chinese citizens in the Philippines".