The two suspects, Guo Jing and her husband, Li Qingliang, have been taken into custody by Cebu police. However both invoked immunity as they claim to be diplomats, according to the police.

A source close to the diplomatic mission said Guo worked at the visa service department. The police suspect Li was the shooter and have yet to determine the extent of the wife's involvement. A 45 calibre gun was found at the scene.

Song was shot at the back of his neck "but the wound was through and through", said Cebu Police Office director Mariano Batiancela.

Sun was also shot in the neck while Li suffered a head wound, according to a police statement.

"The investigation is ongoing. We have not talked to the suspects or the consul general because we are waiting for an official from the Chinese embassy in Manila who is on his way here now," he said.

RECAP: 'I dived under the counter': terrified waitress at Cebu restaurant tells of fatal shoot-out that left China envoy hospitalised, two consulate staff dead

The Ministry of Foreign Affairs declined to comment and calls to the Cebu consulate went unanswered.

A senior government official in the Philippines confirmed to the South China Morning Post that the Chinese government has sought full diplomatic immunity for all its staff involved in the investigation. 

The official, who asked not to be named, said full diplomatic immunity meant “they are immune from arrest, prosecution and detention, under the Vienna Convention”. 

The official said they were awaiting word from the foreign affairs department on whether they could still proceed with questioning suspects and other Chinese consular staff who had witnessed the killings. 

China and the Philippines have an agreement “that broadened the Vienna Convention and granted full immunity even to consular officials of both countries”, the source said. 

The two countries also have an extradition treaty, the source added.

While the safety of Chinese diplomats has drawn attention in recent years given the country's more proactive role in conflict zones, such violence among Chinese overseas diplomatic missions is extremely rare.

Several local businessmen said Song was not well known among locals because he was new to Cebu. Many met him for the first time at a banquet last month to celebrate China's National Day.

The shooting took place after midday inside the popular Lighthouse Restaurant where Song was reportedly celebrating his birthday, although the purpose of the gathering had not yet been confirmed by the police.

Media reports said nine people in all, including the two suspects, were present at that time.

Lighthouse manager Stephen John Patero said the shooting occurred in a private room of the upmarket restaurant, which is a favourite for local politicians.

"We did not really see the actual shooting. They were inside a private function room. There was a series of gunshots," Patero told Agence France-Presse. But he said waiters who served them beforehand had heard the guests shouting at each other.

"They are all friends who apparently figured in an argument," he said, citing the waiters.

Restaurant cashier Remedios Rivalde, 27, said she was outside the function room when she heard gunshots, Agence France-Presse reported.

"I dived under the counter and covered my ears. Then there were other shots that followed."

She said the reservation had been made shortly before lunch for the consul general's birthday, and the group had ordered a banquet that included popular local delicacies such as tuna head, shrimps and roasted pork, Agence France-Presse reported.

"They ordered a lot of food, but no liquor," she said.

The Philippine Daily Inquirer reported surveillance camera footage showed Li walking out of the restaurant shortly after the shooting, leaving his firearm behind, which his wife later hid.

A source close to the consulate said ambassador to the Philippines Zhao Jianhua was aware of the tragedy and expected to arrive in Cebu later last night.