(CNN) -- Scores of people in the Philippine capital held a demonstration Friday to protest China's increasingly bellicose rhetoric about a monthlong naval standoff between Beijing and Manila over a disputed lagoon in the South China Sea.
Gathered in front of the Chinese Embassy in Manila, the demonstrators waved Philippine flags and held up banners displaying slogans like "Stop China's aggression now."
The protest follows a string of signals from China this week suggesting that the Asian economic and military giant is losing patience with its smaller neighbor's insistence that it has sovereignty over the contested area, the Scarborough Shoal.
The PLA Daily, the official Chinese military newspaper, has warned that the country's armed forces would not allow anyone to challenge China's sovereignty over the tiny island outcrop, which Beijing calls Huangyan Island and Manila calls Panatag Shoal.
"We want to say that anyone's attempt to take away China's sovereignty over Huangyan Island will not be allowed by the Chinese government, people and armed forces," the newspaper said, according to Xinhua, the state-run news agency.
The planned protests in the Philippines prompted China to advise its citizens there to remain indoors, state media reported.
"The Philippines has been repeatedly making strong-worded remarks over the Huangyan Island," said Ministry of Foreign Affairs spokesman Hong Lei.
"China hopes the Philippines will not take any actions to magnify the dispute in a way that may affect the relationship between the two countries."
Chinese travel agencies have suspended tours to the Philippines, according to state media, and China's Vice Foreign Minister Fu Ying said earlier this week that she was not optimistic about the situation in the South China Sea after meeting Philippine officials.
Raul Hernandez, a spokesman for the Philippine Department of Foreign Affairs, said that officials "are endeavoring to undertake a new diplomatic initiative, which we hope will help defuse the situation."
The standoff over the lagoon, some 130 miles (200 kilometers) from the Philippine island of Luzon, began last month when Manila sent its largest naval vessel to the area to investigate Chinese fishing boats it says were illegally fishing there.
Chinese surveillance vessels then arrived on the scene, preventing the Philippine navy sailors from arresting the fishermen and starting the tense maritime deadlock. China says the fishing boats were just seeking shelter in the lagoon.
Both countries have since shuffled different vessels in and out of the area, saying they want a diplomatic solution to the problem. But neither side is willing to back down altogether.
Analysts believe the area is rich in mineral resources, natural gas and oil -- providing a strong economic subtext to the diplomatic wrangling.
Beijing and Manila are adamant that their territorial arguments are justified.
"They both have claims," said Stephanie Kleine-Ahlbrandt, the North East Asia project director and China adviser for the International Crisis Group. "China goes back centuries, but the Philippines also says it has maps from the 18th century showing it belongs them."
Philippine officials say they want to resolve the dispute through international negotiation. That approach was among the calls from the demonstrators in Manila on Friday.
"We hope that these actions will convince the Chinese government to sit down at a multilateral platform," said Risa Hontiveros, a spokeswoman for the Akbayan Party who participated in the protest.
But China rejects this because it has a long-standing distrust of Western-dominated international mediators, Kleine-Ahlbrandt said.
"There are a dozen ships in a standoff there right now," she said. "Both sides are really using this for all it is worth, whipping up nationalistic sentiment -- what is needed is something to de-escalate the situation."
The standoff comes against the backdrop of the political scandal in China surrounding the former high-ranking Communist Party official Bo Xilai and ahead of a once-in-a-decade leadership transition due later this year.
CNN's Jethro Mullen, Stan Grant and Paul Armstrong contributed to this report.