A convoy of civilian boats planning to deliver provisions to Filipino fishermen and troops in the disputed South China Sea aborted the trip on Sunday after “constant shadowing” by Chinese vessels, the organizer said.

The “Christmas convoy”, which departed the Philippines’ western island of Palawan in the early hours of Sunday, was being led by dozens of volunteers on two boats carrying food, water and other donations.

It had already changed course after a confrontation between Philippine and Chinese vessels earlier in the day.

The Atin Ito group said it was “erring on the side of caution” in consultation with the Philippine Coast Guard and had decided to return to El Nido in Palawan “after the constant shadowing of four Chinese vessels”.

The Chinese vessels included two Navy ships, one coast guard and one cargo ship, the group said in a statement.

Fishermen in 40 wooden outrigger boats who had joined the convoy would also return to shore, said Emman Hizon of Atin Ito.

“Even going back to El Nido, they are still being shadowed by two Chinese Navy and one Chinese Coast Guard”.

The Philippine Coast Guard escorted the convoy as it traveled through the hotly contested Spratly Islands in the South China Sea, which China claims almost entirely.

The Philippines has outposts on nine reefs and islands in the Spratlys. It was not immediately clear how far the convoy got before turning back.

Atin Ito Coalition, or “It is Ours” Coalition, said previously the convoy aimed to highlight the living and working conditions of Filipino fishermen and personnel, and to defend the country’s maritime territorial rights.

The convoy had planned to go past Second Thomas Shoal, where a handful of Filipino troops are stationed on a grounded warship, on its way to the Philippine-held Nanshan Island where donations would be left.

A collision and confrontation between Philippine and Chinese vessels near the reef, however, forced organizers to reroute the convoy to head straight towards Nanshan.

Both countries’ coast guards blamed the other for Sunday’s collision, the latest in an escalating series of such conflicts in the disputed sea. Manila also accused Chinese vessels of firing water cannons at its boats.

Rafaela David, a member of the Atin Ito Coalition that organized the convoy, said earlier the Chinese actions had endangered “the safety of our civilian supply mission”.

“(It) also runs counter to the principles of human rights that the international community upholds, and our rightful claims to the West Philippine Sea”, said David, who is also president of the left-wing political party Akbayan.

The people in the convoy included fisherfolk, students and youth leaders.

“We joined the (convoy) … because we need to fight for what is rightfully ours,” said Maureen Ignacio, whose family depends on fishing in Bataan province, near Manila.

Organizers had originally hoped to visit the troops stationed on the BRP Sierra Madre, a World War II-vintage warship grounded on Second Thomas Shoal in 1999.

The rusty hulk has long been a flashpoint for Manila and Beijing, with several recent incidents involving Philippine and Chinese vessels straining diplomatic relations.

But the National Security Council advised the organizers to pass only within the “general vicinity” of the reef, where Chinese vessels regularly patrol.