The United States has offered to escort Manila's resupply missions to outposts in the disputed South China Sea, the Philippine military chief said Thursday, following Beijing's intensifying efforts to block them. 

General Romeo Brawner said the Philippines would not take up the offer until it reached a point when they could not deliver life-saving provisions and troops were "on the verge of dying".

"We're happy that the US has given us a range of options including that of joining or escorting us for the ROREs (rotation and resupply missions)," Brawner told a news conference after meeting with US Indo-Pacific Commander Admiral Samuel Paparo in the northern city of Baguio. 

Paparo told reporters that "we stand ready", without offering further details.

There has been a series of escalating clashes between Philippine and Chinese vessels in the past year during resupply missions to Filipino troops, coast guard personnel and fishermen at Second Thomas, Sabina and Scarborough shoals.

China claims most of the South China Sea despite an international ruling that its assertion has no legal basis, and defends its actions against Philippine vessels as lawful and proportional. 

Philippine and Chinese vessels have collided twice this month near Sabina Shoal, where the Philippine Coast Guard has anchored a ship to prevent China seizing the ring of reefs.

A Filipino sailor lost a thumb in a June 17 clash at Second Thomas Shoal when Chinese coast guard members wielding knives, sticks and an axe foiled a Philippine Navy attempt to resupply its troops there.

The incidents have fuelled concerns that the United States, a longtime ally of the Philippines, could be drawn into armed conflict with China due to its mutual defence treaty with Manila. 

Brawner said Washington and Manila have discussed options for keeping Filipino personnel supplied with essential provisions even as Chinese ships patrol the waters around them. 

For now, however, Brawner said the Philippines had not exhausted its options and it would continue to conduct resupplies "unilaterally". 

"If nothing works then that's the time we can ask for help," Brawner said.

Brawner said Manila had used a helicopter to deliver supplies to the Philippine Coast Guard's BRP Teresa Magbanua, which has been anchored at Sabina Shoal since April to prevent China seizing it. 

Paparo told reporters in Manila on Tuesday that the  "escort of one vessel is an entirely reasonable option within our Mutual Defence Treaty"