HONG KONG >> Philippine officials said Monday that President Rodrigo Duterte planned to declare a marine sanctuary and no-fishing zone at a lagoon within Scarborough Shoal, a reef China seized in 2012.

The announcement followed Duterte’s meeting with President Xi Jinping of China on the sidelines of the Asia-Pacific Economic Cooperation summit meeting in Peru over the weekend. It was unclear whether the plan had Xi’s backing; the Philippine national security adviser, Hermogenes Esperon Jr., said in a statement Monday that creating the proposed sanctuary was “a unilateral action.”

The plan comes about four months after the Philippines largely won an international arbitration ruling that had challenged China’s seizure of Scarborough Shoal. It also comes as Duterte has tried to reset frayed relations with China.

Duterte’s communications secretary, Martin Andandar, quoted Xi as having called for a “favorable environment” at Scarborough Shoal, which both countries claim.

Experts said Monday that it would be difficult to assess the feasibility of Duterte’s plan without further details, and that a crucial question was whether China would be involved in the implementation or enforcement of the proposed sanctuary.

The South China Sea is facing an overfishing crisis, and scientists say that China’s campaign to turn seven disputed reefs into artificial islands and build military facilities on some of them is damaging crucial spawning grounds. They say the establishment of port facilities at the new islands may also encourage Chinese fishing fleets to travel farther afield from the Chinese mainland, putting even greater pressure on beleaguered fish stocks.

Ian J. Storey, a South China Sea expert in Singapore, said that scientists had been seeking multilateral conservation agreements in the sea for decades. Despite that, Storey said the idea had so far been a diplomatic nonstarter because there are so many overlapping territorial claims.

Storey said that a multilateral management plan of the Scarborough lagoon had a chance to succeed and would be a logical extension of the reconciliation between China and the Philippines. But he said China would almost certainly not respect a unilateral fishing ban by the Philippines.

The Philippine proposal is “a unilateral initiative,” Storey said, “and unilateral initiatives in the South China Sea have a history of going nowhere.”