Beijing warned Manila that it is "hard to be optimistic" about the impasse over Huangyan Island, and authorities say they are prepared for any escalation of the situation by Manila.

Vice-Minister of Foreign Affairs Fu Ying on Monday summoned Alex Chua, charge d'affaires of the Philippine embassy in Beijing. It was the third summons following previous ones on April 15 and 18.

Analysts said the Monday summon shows the strongest protest from Beijing against Manila's rival claims over China's territorial island since the island impasse started on April 10.

Despite the two summons last month, "the Philippine side has not realized that it is making serious mistakes and instead is stepping up efforts to escalate tensions", said the vice-minister.

Manila's moves are "severely damaging the atmosphere of the bilateral relations between China and the Philippines", Fu said. "Therefore it is hard for us to be optimistic about the situation."

Manila has been playing with fire and trying to push the bottom line of Beijing, and the Monday summon serves as a sturdy protest against Manila's recent provocations, said Yang Baoyun, a professor of Southeast Asian studies at Peking University.

"The neighboring countries' decisions to not take sides on the issue show that the Philippine's territorial claim has received little support. Now the Philippines also finds it hard to change its stance overnight," Yang said.

Huangyan Island has been an integral part of China's territory for centuries, and Beijing expects Manila not to misjudge the situation and not to "escalate tensions without considering the consequences".

On Tuesday, Beijing also slammed Manila's recent attempts to raise the island dispute before international tribunals as well as some remarks that called on judgment from a third party.

"Isn't it a weird thing among international affairs to raise a country's territory to international tribunals? How chaotic the world would be?" Chinese Foreign Ministry spokesman Hong Lei said at a daily news conference.

China's sovereignty over the island is justified in both historical records and legal documents, Hong said.

"Whatever the Philippine side said and did about Huangyan Island does not change the basic fact that the island belongs to China," he added.

On April 10, a Philippine warship entered the island's territorial waters, dispatched personnel to harass Chinese fishing boats and attempted to detain Chinese fishermen.

Beijing said the move infringed on China's sovereignty. Two Chinese patrol ships in the area later came to the fishermen's rescue, and the warship left.

But the impasse continued in the wake of the incident as the Philippine side continued to send government vessels to the lagoon of Huangyan Island.

Manila also repeatedly made erroneous remarks that mislead the public in the Philippines and the international community and played up public feelings.

Fu urged Manila to withdraw all Philippine vessels in the island waters and warned Manila not to disturb operations by Chinese fishing boats as well as the Chinese government's law enforcement vessels.

Philippine vessels were reportedly still in China's territorial waters on Tuesday.

An opinion article in Tuesday's People's Daily Overseas Edition warned the Philippine side not to take China's sincerity as a chance to bully China.

Given recent challenges by the Philippines, China's patrol ships will remain alert in the waters of Huangyan Island, and Chinese fishery administration vessels will also ensure that Chinese fishermen can perform their jobs in their traditional fishing areas without interference, Fu added.