China's coastguard said it had taken measures against Philippine vessels in disputed waters of the South China Sea on Saturday, while the Philippines decried the moves, including the use of water cannons, as "irresponsible and provocative".

China's actions led to "significant damage" and injury to personnel on a civilian boat hired to resupply troops, the Philippine task force on the South China Sea said in a statement.

The incident occurred in the Second Thomas Shoal and Spratly Islands waters, according to the Chinese coastguard. The shoal is home to a small number of Filipino troops stationed on a warship that Manila grounded there in 1999 to reinforce its sovereignty claims.

China claims almost the entire South China Sea, including the Second Thomas Shoal, which is within the Philippines' 200-mile (320-km) exclusive economic zone, and has deployed vessels to patrol the disputed atoll. A 2016 ruling by the Permanent Court of Arbitration found that China's sweeping claims have no legal basis.

The civilian boat was being escorted by two Philippine navy ships and two Philippine coastguard vessels, according to a statement from the Philippine military.

A Philippine coastguard vessel was "impeded" and "encircled" by a Chinese coastguard vessel and two Chinese maritime militia vessels, the Philippine coastguard said in a separate statement.

VESSEL ISOLATED

As a result, the Philippine coastguard vessel was "isolated" from the resupply boat by the "irresponsible and provocative behaviour" of the Chinese maritime forces, the agency said.

Washington "stands with its ally the Philippines and condemns the dangerous actions" of China, State Department spokesperson Matthew Miller said in a statement.

"The PRC’s actions are destabilizing to the region and show clear disregard for international law," Miller said, referring to the People's Republic of China.

Gan Yu, a spokesperson for China's coastguard, said the Philippines had broken a promise to remove the grounded vessel and sent two coastguard ships and a supply ship into the Second Thomas Shoal waters, 18 days after the last round of supplies.

China has not said who promised the removal or when that promise was made. The Philippine defence ministry, foreign ministry and military leaders have repeatedly said there was no such promise.

Gan said the Philippines had on Saturday infringed and provoked trouble, and deliberately undermined the peace and stability of the South China Sea.

The Philippine vessels ignored China's repeated warnings and route controls and forced their way in, Gan added. The China coastguard implements regulations in accordance with laws and handles matters in a reasonable, legal, and professional manner, he said.

"If the Philippines continues to act unilaterally, China will continue to take resolute measures to safeguard its territorial sovereignty and maritime rights and interests," China's foreign ministry said.

"All consequences caused by this shall be borne by the Philippines."

But the Philippines will not be deterred "by veiled threats or hostility" from exercising its legal rights over its maritime zones, including the Second Thomas Shoal, its task force said.