The Permanent Court of Arbitration in The Hague is to rule in a dispute between the Philippines and China over maritime claims in the South China Sea - particularly who has the right to exploit resources in the strategic territory.
The ruling on Tuesday is expected to further increase tensions in the region, where China's increased military assertiveness has spread concern among its smaller neighbours and is a point of confrontation with the United States.
China has boycotted the court, saying it does not have jurisdiction to decide on the matter and has campaigned for months to discredit the outcome.
In advance of the ruling, the China Daily newspaper, which is published by the government, topped its front page on Tuesday with a picture of Woody Island in the South China Sea emblazoned with the words: "Arbitration invalid".
State-run news agency Xinhua included headlines such as: "South China Sea arbitration abuses international law: Chinese scholar".
The Philippines embassy in China warned its citizens to be "careful" due to tension before the ruling and to avoid political debate. The embassy also urged its citizens to carry identification papers "at all times" and report any threat received to the embassy and Chinese police.
Key sea lane
China asserts sovereignty over almost all of the South China Sea, a strategic waterway through which more than $5 trillion of world trade is shipped each year, despite rival claims from the Philippines and other Southeast Asian nations.
The US says it wants the crucial sea lane to be treated as international waters.
Both Beijing and Washington have accused each other of provocations in the South China Sea.
Al Jazeera's Adrian Brown, reporting from Beijing, said China's leaders would "simply shrug off the tribunal's rulings.
"In recent weeks, they've labelled the court illegal, irrelevant and said it had no jurisdiction. And they appear to care little about Washington's renewed threats and warnings."
Karl Friedhoff, an Asian affairs expert at the Chicago Council on Global Affairs, said China had made it clear that it was in no "mood for negotiation".
"They are really trying to get access to the open ocean, so they can start to really project their power," he told Al Jazeera.
Friedhoff added, however, that if Beijing decided to press the matter aggressively with the Philippines and other Southeast Asian countries, "then it is going to undercut the soft power that China has worked so hard to grow".
Even if Beijing ignores the court's decision, it is significant as it will be the first time that a legal challenge has been brought against China in the dispute.
"While China insists that it does not care about the decision, its actuations clearly reveal that it is worried about its image," Alexander Yano, a former diplomat and top military commander in the Philippines, told Al Jazeera.
"Beijing is certainly concerned about the negative psychological impact in the international arena should the Hague court rules in favor of the Philippines."
China's expanding presence
Including the Philippines, the dispute draws in a total of five countries with overlapping claims in the 3.5 million square kilometre sea, where China has been expanding its presence by building artificial islands and dispatching patrol boats that keep fishing vessels from other countries away.
The arbitration court ruling will not decide on matters of territorial sovereignty, but will apply the UN Convention on the Law of the Sea in determining which countries can claim economic exploitation rights, based on geographic features.
The court has no power of enforcement, but a victory for the Philippines could spur Taiwan, Vietnam, Malaysia and Brunei, which also have overlapping claims, to file similar claims.
