Former Philippine leader Fidel Ramos said Tuesday he would meet contacts with links to Chinese President Xi Jinping during a trip to Hong Kong intended to improve ties between Manila and Beijing.

Relations have cooled since a UN-backed tribunal ruled last month that China's claims over most of the South China Sea were invalid, in a sweeping victory for the Philippines which brought the case.

Ramos -- a longtime advocate of closer Philippine-Chinese ties -- was sent as a conciliatory envoy by current Philippine president Rodrigo Duterte, but has been vague about his itinerary.

"My job is to look for some old friends who have links to the high officials in Beijing, although most of them have retired," the ex-president told reporters Tuesday after arriving Monday night.

Asked if they had links to Xi, Ramos replied: "I'm sure they have."

Ramos, 88, said he was not sure if he would be travelling on to Beijing, adding that it depends on instructions from Manila.

Ramos, who described himself an "optimist", was also not clear about who he would be meeting.

The only contact he named was Wu Shicun, president of China's National Institute for South China Sea Studies.

"I'm here on a fishing expedition and will play a little golf," Ramos said in describing his itinerary.

Duterte's spokesman Ernie Abella has said the trip could "pave the way for future diplomatic talks".

Philippine-Chinese ties have frayed in recent years due to growing tensions over Beijing's claims to almost all the South China Sea.

The Philippines, Brunei, Malaysia, Taiwan and Vietnam have competing partial claims and are perturbed by China's aggressive moves to assert its sovereignty such as by reclaiming islands and building airstrips.

China has angrily refused to recognise last month's tribunal decision.

Ramos, who was president from 1992-1998, took a laid-back approach to Tuesday's press conference at the Philippine consulate, which was also attended by his wife and grandson.

He insisted reporters come up and stand beside him to ask questions, putting his arm around the female ones and telling journalists to "smile".