The Philippine government has presented a strongly-worded protest to the Chinese ambassador over the Chinese coast guard’s use of a water cannon against a Filipino supply boat in the disputed South China Sea.

The Philippine military has condemned the Chinese coast guard ship’s “excessive and offensive” use of a water cannon to block a Filipino supply boat from delivering a new batch of troops, food, water and fuel to the Philippine-occupied Second Thomas Shoal in the disputed waters.

The United States, the European Union and their key allies including Australia and Japan expressed support to the Philippines and concern over the Chinese ship’s actions.

Washington renewed a warning that it is obliged to defend its long-time treaty ally if Filipino public vessels and forces come under an armed attack including in the South China Sea.

On Monday, the Philippine coast guard and diplomatic officials held a news conference at which they revealed videos and photographs which they said showed six Chinese coast guard ships and two militia vessels blocking two Philippine navy-chartered civilian boats taking supplies to the Philippine forces at Second Thomas Shoal.

One supply boat was hit with a powerful water cannon by the Chinese coast guard, the Philippine military said.

Only one of the two Philippine boats managed to deliver food, water, fuel and other supplies to the Philippine forces guarding the shoal, the officials said.

During the confrontation, two Philippine coast guard ships escorting the supply boats were also blocked by the Chinese coast guard ships at close range and were threatened with water cannons.

Three Chinese navy ships stood by at a close distance at one point, Philippine coast guard Commodore Jay Tarriela said.

“This was like a David and Goliath situation,” Jonathan Malaya of the National Security Council said.

Mr Malaya emphasised that the Philippines would not withdraw its forces from Second Thomas Shoal.

Department of foreign affairs spokesperson Teresita Daza said China’s ambassador to Manila, Huang Xilian, was summoned and handed a diplomatic protest by Philippine Undersecretary Theresa Lazaro.

In it, the Philippines told China to stop its illegal actions against Philippine vessels in the South China Sea, stop interfering in legitimate Philippine activities, and abide by international laws, including the 1982 UN Convention on the Law of the Seas, Ms Daza said.

The Chinese coast guard acknowledged its ships used water cannons against the Philippine vessels, which it said strayed without authorisation into the shoal, which Beijing calls Ren’ai Jiao.

It accused the Philippines of reneging on a pledge to remove the grounded Filipino warship from the shoal.

“In order to avoid direct blocking and collisions when repeated warnings were ineffective, water cannons were used as a warning. The on-site operation was professional and restrained, which is beyond reproach,” the Chinese coast guard said.

“China will continue to take necessary measures to firmly safeguard its territorial sovereignty.”

China has long demanded that the Philippines withdraw its naval personnel and tow away the still-commissioned but crumbling ship, the BRP Sierra Madre. The ship was deliberately marooned on the shoal in 1999 and now serves as a fragile symbol of Manila’s territorial claim to the atoll.

The tense confrontation on Saturday was the latest flare-up in the long-seething territorial conflicts involving China, the Philippines, Vietnam, Malaysia, Taiwan and Brunei.

The protest underlines how the Chinese coast guard ship’s action violated international regulations aimed at avoiding collisions at sea and the 1982 UN Convention on the Law of the Sea, said one official.

The disputes in the South China Sea, one of the world’s busiest sea lanes, have long been regarded as an Asian flashpoint and a delicate fault line in the rivalry between the United States and China in the region.

China claims ownership over virtually the entire strategic waterway despite international rulings that invalidated Beijing’s vast territorial claims, such as that in 2016 by the Permanent Court of Arbitration, an international body based in The Hague. China rejects that ruling.