An aerial file photo taken though a glass window of a Philippine military plane shows the alleged on-going land reclamation by China on Mischief Reef in the Spratly Islands in the South China Sea, west of Palawan, Philippines, May 11, 2015. REUTERS/Ritchie B. Tongo/Pool/Files

China's claims to the disputed South China Sea will come under international legal scrutiny for the first time this week, but while Beijing has officially refused to take part in the case filed by the Philippines at a U.N. tribunal, it has made its presence felt.

Indeed, Manila's international legal team was heading to the Permanent Court of Arbitration in The Hague to initially argue that the five-judge panel has jurisdiction to hear the case, Philippine Foreign Ministry officials told Reuters.

That is because of concerns China raised in a public position paper in December about the tribunal's jurisdiction over the matter, according to court statements.

A little-noticed decision by the tribunal's panel in April acknowledged China's objections and announced that a hearing on jurisdiction from July 7-13 would be held first.

Manila filed the case in 2013 to seek a ruling on its right to exploit the South China Sea waters in its 200-nautical mile exclusive economic zone (EEZ) as allowed under the U.N. Convention on the Law of the Sea (UNCLOS).

While legally binding, any decision that favours the Philippines would be unenforceable because there is no U.N. body to police such rulings, legal experts said.

Nevertheless, such a ruling would be a diplomatic blow to Beijing and might prompt other claimants to the South China Sea to take similar action, legal experts and diplomats said.

The case is being closely watched by Asian governments and Washington given rising tensions in the South China Sea, especially in the Spratly archipelago, where China is creating seven artificial islands that will allow its navy to project power deep into the maritime heart of Southeast Asia.

China claims most of the waterway, including many reefs and shoals that Manila considers are within its EEZ. Parts of the EEZ contain rich fishing grounds and energy deposits.

Vietnam, Malaysia, Brunei and Taiwan also have claims to the South China Sea, through which $5 trillion in ship-borne trade passes every year.

Effectively taking part

Some international legal scholars and South China Sea experts said China was effectively taking part in the case even though it had officially refused to do so.

"It appears the tribunal panel is bending over backwards to accommodate China's interests and appear even-handed to both the Philippines and China," said Ian Storey, a South China Sea expert at Singapore's Institute of South East Asian Studies.

Experts said that did not mean the judges would find in Beijing's favour.

"They are being as fair as they can ... they seem to sense China will scrutinise every word in any final ruling," said one legal scholar following the case.

When asked to comment, tribunal officials referred Reuters to statements on its website.

Without China's permission, Manila cannot seek a ruling at the International Court of Justice in The Hague on the sovereignty of the disputed territory, legal scholars said.

Instead, Manila has invoked dispute settlement procedures under UNCLOS, a system that allows for arbitration even when one side objects and refuses to participate.

The Law of the Sea does not rule on sovereignty but it does outline a system of territory and economic zones that can be claimed from features such as islands, rocks and reefs.

The Chinese position paper last December said the "essence" of the Philippine case was sovereignty, and therefore beyond the scope of the tribunal.

Storey said the hearing on jurisdiction could delay any final ruling by six to 12 months, meaning the case could linger beyond the single term of Philippine President Benigno Aquino, which ends next June.

Aquino has been a key figure behind the legal challenge, at times drawing China's ire by comparing its South China Sea claims to Nazi Germany's expansionism before World War Two.

China will reject outcome

Chinese diplomats and legal experts have been following developments closely and taking outside opinions, according to sources with knowledge of Beijing's approach to the case.

Some of that work has been handled by the Chinese embassy at The Hague, which has established a formal line of communication with the tribunal, they said.

Tribunal statements and the rules of the case reviewed by Reuters confirm that China can communicate with the tribunal via its ambassador to The Hague, while the court also updates China on procedural moves and opportunities for submissions.

Despite the exchanges, China still planned to reject any decision that favoured Manila, the sources said.

Chinese Foreign Ministry spokeswoman Hua Chunying told a regular briefing on Thursday that the "unilateral" arbitration was "a political provocation in the guise of law that seeks to deny China's national sovereignty in the South China Sea".

Charles Jose, the Philippine Foreign Ministry spokesman, disagreed: "The court is a fundamental first step towards a peaceful and rules-based resolution of the issue," he said.

Zha Daojiong, a political scientist at Peking University, said he believed Beijing's strategy of not taking part and then refusing to accept any judgement was set.

"Without China's participation, any ruling can only be an opinion," he added.