The Philippines deployed a second vessel to tiny islands in the South China Sea on Thursday in a bid to protect its sovereignty in an increasingly tense territorial standoff with China.
Authorities said a coast guard boat joined the Philippines' biggest warship at Scarborough Shoal, where two Chinese surveillance vessels were protecting a group of Chinese fishermen from being arrested.
"It has arrived in the area. It is there to support our navy and to show our flag," foreign affairs department spokesman Raul Hernandez told reporters, referring to the 56-metre-long (184-foot) search and rescue coast guard vessel.
"It is mandated to protect our seas."
However Hernandez also emphasised the Philippines was intent on ending the standoff peacefully, and quickly.
"We are confident the two sides will find a diplomatic solution as they are committed to finding one," he said.
"We want this to be resolved immediately. Our people are there, the Chinese fishermen are there. It is hot and they could run out of food so we want this to be resolved as soon as possible."
The dispute began on Sunday when Philippine authorities found eight Chinese fishing boats at the shoal, a group of tiny islands and reefs 124 nautical miles west of the country's main island of Luzon.
The Philippines accused the fishermen of being there illegally, asserting the area was Philippine territory because it was within the country's 200-nautical-mile exclusive economic zone, as recognised by international law.
However China claims all of the South China Sea as its own, even waters up to the coasts of other countries, and Chinese authorities insisted the fishermen were allowed to be at the shoal.
Competing claims to the South China Sea have long been regarded as one of Asia's potential flashpoints for military conflict.
Aside from the Philippines and China, Taiwan, Vietnam, Malaysia and Brunei also have competing claims to the waters.
More than 70 Vietnamese sailors were killed in 1988 when China and Vietnam battled for control of the Spratlys, an archipelago south of Scarborough Shoal.
The sea holds huge economic and political significance, as it is believed to sit atop vast oil and gas resources, is home to vast fishing grounds and hosts shipping lanes that carry a third of the globe's maritime trade.
In the latest flare-up in tensions, the Philippines deployed its navy flagship vessel to Scarborough Shoal immediately after the Chinese fishermen were discovered there.
But the two Chinese surveillance vessels appeared on the scene on Tuesday and blocked the Philippine warship from arresting the fishermen, who had reportedly hauled in corals, live sharks and some endangered species.
"For us, this is illegal fishing, illegal poaching and that is why our navy is there to protect our sovereignty and assert our rights," Hernandez said.
The Chinese embassy in Manila released a statement on Wednesday insisting the waters belonged to China and ordering the Philippine warship to leave immediately.
In Beijing, foreign ministry spokesman Liu Weimin accused the Philippines of "harassing" the Chinese fishermen and said a protest had been lodged.
"We urge the Philippine side... not to make new troubles and create conditions for the friendly relations of the two countries," Liu said.
The Philippines and Vietnam complained last year of increasingly aggressive acts by China in staking its claim to the South China Sea.
The Philippines accused Chinese vessels of firing warning shots at Filipino fishermen, as well as harassing an oil exploration vessel and placing markers on islets within Philippine territory.
However this week's standoff is the highest-profile in recent years.