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, officials said.

National Bureau of Investigation (NBI) director Jaime Santiago told a news conference the men used a drone to document goings-on at a naval detachment, coast guard ships, an air base, a naval base, and a dockyard in Palawan province, the closest major land mass to the Spratlys.

"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.

Two other Chinese men were 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 and two Filipino associates suspected of spying on military and police camps -- allegations that were dismissed by the Chinese embassy in Manila.

Officials did not say who employed the suspects.

NBI cybercrime unit chief Jeremy Lotoc said Thursday an unnamed "foreign national" was giving orders to Chinese software engineer Deng Yuanqing, who was detained earlier this month.

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.

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.

It described on Saturday 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".