An international group of legal experts and lawyers have signed a legal opinion document questioning an arbitration tribunal's jurisdiction in a case filed against China by the Philippines.

They have also voiced concern over the suitability of the tribunal to handle such an issue without considering the historical and political context, according to Hong Kong barrister Daniel Fung Wah-kin.

"We hope to protect the integrity and reputation of the tribunal and the whole international law system," Fung said.

In 2013, the Philippines unilaterally filed compulsory arbitration under the United Nations Convention on the Law of the Sea challenging China's sovereignty in the area.

Beijing has refused to be part of the arbitration and says the tribunal has no jurisdiction, while Manila has showed no indication of returning to bilateral negotiations.

Others signing the document include Tony Carty, a British scholar and professor of international law at Tsinghua University, and Natalie Klein, professor and dean of Macquarie Law School in Sydney.

Fung said they are awaiting a reply from the tribunal and have asked for an opportunity to present the case orally.

Although the full text of the document has not been released to the media, its main point is that the tribunal has no jurisdiction over sovereignty disputes and maritime delimitation, as the UN Convention on the Law of the Sea does not issue such judgments.

Huang Yao, dean of the School of Law at Sun Yat-sen University in Guangzhou, Guangdong province, said the tribunal has imposed its jurisdiction but has no legitimacy.

Fung said that as Chinese people have had links to the islands in the South China Sea for more than 2,000 years, the tribunal should carry out adequate research into the country's rights and interests before making any judgment.

"These questions should be settled by diplomatic negotiations in treaty form," Fung said.

Kuen-chen Fu, dean of the South China Sea Institute at Xiamen University, said the tribunal should take the document for reference, but it has no obligation to accept it.