China has stationed several ships near a disputed atoll in the South China Sea, Philippine officials say, preventing its fishermen from accessing traditional fishing grounds and raising tensions in the volatile region.
Eugenio Bito-onon Jr, the mayor of nearby Pagasa Island in the Spratly Islands, said China had deployed up to seven ships to Quirino Atoll, also known as Jackson Atoll.
But China's Foreign Ministry said on Wednesday that its vessels in the area were deployed to tow a grounded ship, and that these vessels had since left the waters.
The Spratlys are the most contested archipelago in the South China Sea, a resource-rich region and critical shipping lane linking North Asia to Europe, South Asia and the Middle East.
"This is very alarming," Mr Bito-onon Jr told Reuters. "Quirino is on our path when we travel from Palawan to Pagasa. It is halfway and we normally stop there to rest.
"I feel something different. The Chinese are trying to choke us by putting an imaginary checkpoint there. It is a clear violation of our right to travel, impeding freedom of navigation," he said.
Fishermen told the mayor that one Filipino boat had run aground in the area and was still there, but was not being harassed by the Chinese vessels.
The Philippine military said it was trying to verify the presence of Chinese ships near Jackson Atoll, where a Chinese warship allegedly fired warning shots at Filipino fishermen in 2011.
"We know there are Chinese ships moving around the Spratly area," spokesman Brigadier-General Restituto Padilla said.
"There are also ships around Second Thomas Shoal, so we want to make sure if the presence is permanent."
Second Thomas Shoal is where the Philippines navy has been occupying and reinforcing a rusting ship that it ran aground in 1999 to bolster its claims to the disputed reef.
Tensions mount over land reclamations
A military source from Palawan said a surveillance plane had seen four to five ships in the vicinity of Jackson Atoll last week.
The source could not say if the ships were passing through or permanently stationed there because the area is close to Mischief Reef, where China is building an artificial island.
The Philippines Star newspaper quoted an unidentified fisherman as saying Chinese boats chased them away when they tried to enter the area last week.
Almost $US5 trillion in global trade passes each year through the South China Sea, which is also believed to hold huge deposits of oil and gas.
China claims almost all of the sea, but the Philippines, Brunei, Malaysia, Taiwan and Vietnam also have claims on the strategic waters.
Tensions in the region have been building recently, with the United States and others protesting against Beijing's land reclamations, along with the recent deployment of surface-to-air missiles and fighter jets in the Paracel Islands.
US Defence Secretary Ash Carter warned China against what he called "aggressive" actions in the region, saying there would be "specific consequences" to militarisation of the South China Sea.
In response, Chinese Foreign Ministry spokesman Hong Lei urged Washington to "stop exaggerating and sensationalising" the issue.
For its part, Beijing has been angered by "freedom of navigation" air and sea patrols the US has conducted near the islands it claims and says it needs military facilities for its self-defence.