A convoy of civilian boats planning to deliver provisions to Filipino fishermen and troops in the disputed South China Sea left the Philippines on Sunday but changed course after a confrontation between Philippine and Chinese vessels. 

Fishermen in 40 wooden outrigger boats were expected to join the "Christmas convoy" being led by volunteers on two larger vessels carrying food, water, and other donations.

The convoy departed El Nido municipality on the western island of Palawan before dawn on Sunday and had planned to go past Second Thomas Shoal, where a handful of Filipino troops are stationed on a grounded warship.  

A collision and confrontation between Philippine and Chinese vessels near the reef on Sunday, however, forced organizers to reroute the convoy to go directly to the Philippine-held Nanshan Island, where donations would be left.

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 cannon at its boats.

Rafaela David, a member of the Atin Ito Coalition that organized the convoy, said the Chinese actions 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.

Philippine Coast Guard vessels escorted the civilian 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.

AFP correspondents were on board one of the coast guard vessels.

Atin Ito Coalition, or "It is Ours" Coalition, said 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 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.

David said Atin Ito members would decide later if they would travel past the shoal on the way back to Palawan.