About one hour away from Second Thomas Shoal, where the detachment is based, a Chinese coast guard ship marked "1141" twice crossed the bow of the smaller Philippine vessel in an attempt to stop it from proceeding. Another tailed the Filipino boat.
The Chinese radioed the Filipinos, telling them to stop. "You will take full responsibility for the consequences of your action," the voice said in English.
"This is the Republic of the Philippines," replied Philippine navy Lt. Ferdinand Gato, who was in charge of the supply mission. "We are here to provision the troops."
The marines on board the supply boat waved the "V" for peace sign toward the Chinese vessel.
The Filipino captain maneuvered his vessel to shallow waters where the Chinese ships couldn't sail to reach the marooned vessel, BRP Sierra Madre, which has become an awkward symbol of Philippine sovereignty in the remote offshore territory.
On March 9, Chinese vessels blocked a resupply mission to the shoal, called Ayungin by the Philippines.
Philippine air force planes have airdropped life-sustaining food and water at least twice since then.
The confrontation at sea was witnessed by Associated Press journalists and more than a dozen other media members who were invited by the Philippine military to board the government vessel to show what Manila has described as "China's bullying" in the disputed waters.
As they approached the shoal, one of the marines raised the Philippine flag on the supply ship. Once inside the shoal, the marines and the crew applauded and exchanged high-fives.
Gato said he was determined to complete his supply mission despite the Chinese presence. "I will not let them stop us because our marines will starve," he said.
The supply ship carried about 10 tons of food, including rice and canned goods, and water, Gato said. The provisions were placed in sacks and transferred to the marooned ship using ropes pulled with pulleys. The two vessels were surrounded by the calm turquoise waters of the shoal.
China claims almost the entire South China Sea. The two countries were in a two-month standoff at the Scarborough Shoal to the north, which the Chinese eventually occupied after Philippine ships left the area because of a storm in 2012.
The Philippines has questioned China's claims before the International Tribunal on the Law of the Sea.
Vietnam, Malaysia, Brunei and Taiwan also have claims over the territory, which is believe to be rich in oil and gas and is also a major shipping lane.