Hong Kong (CNN) The Philippines has begun sending troops and supplies to an island it controls in the disputed South China Sea , setting the stage for a potential dispute with Beijing.

Plans are underway to reinforce and upgrade facilities on Pagasa Island, in the Spratly Islands chain, senior Philippine military officials told the official Philippine News Agency (PNA).

The country's president, Rodrigo Duterte, last month said he had ordered military personnel to occupy all Philippines-claimed islands in the South China Sea, parts or all of which is claimed by China, Taiwan, Malaysia, Brunei, Vietnam and the Philippines.

While Manila has traditionally been a strong defender of its claims in the disputed waters -- even winning a landmark international ruling throwing out most of China's claims -- Duterte's government has cozied up to Beijing and pushed territorial disputes to the background

It's unclear how China will react to the military build-up. While it's far less aggressive than actions China has taken in the region, the country traditionally does not react well to any territorial challenges.

If there is a negative reaction, Duterte will find out quickly, as he is visiting Beijing Saturday alongside other world leaders for a forum about China's hugely ambitious One Belt, One Road trade and infrastructure project

Aerial view of a reef near Philippines-controlled Pagasa Island in the South China Sea.

Building up

In April, Duterte said he may raise the Philippines flag on Pagasa, also known as Thitu Island, on the country's independence day on June 12.

Pagasa is one of the largest naturally-occurring islands in the Spratly chain, a cluster of islands, islets and more than 100 reefs some 1,000 kilometers (660 miles) from the southernmost tip of mainland China. By comparison, the chain is within 300 kilometers (185 miles) of the Philippines province of Palawan.

China's claims are based on the historical "nine-dash line," which encompasses almost the entirety of the 3.6 million square kilometer South China Sea.

Pagasa has been occupied by the Philippines for decades and falls under the municipality of Kalayaan on neighboring Palawan. While a small civilian population does reside on the island, it is mainly occupied by the Philippines military.

Filipino children hold up a national flag during a 2015 protest on Pagasa island against Beijing's claims in the South China Sea.

That military presence is now being ramped up. Lt. Gen. Raul Del Rosario, head of the Philippines Western Command, said troops and some initial supplies were transported to the island last week, according to PNA.

Full scale construction will take place once all materials are landed, Rosario said. Plans include airstrip expansion, port and power developments, and civilian research projects.

High stakes

While relations between Manila and Beijing may have improved, the South China Sea is resource rich and a crucial shipping route , and no parties have backed away from their claims, meaning tensions could flare up again at any time.

China has continued militarizing and building up the territories it controls , reclaiming land to turn sandbars into islands, and equipping them with airfields, ports and weapons systems.

Under US President Barack Obama's so-called "pivot to Asia," the US was a strong supporter of countries attempting to resist Chinese expansion in the South China Sea, conducting regular freedom of navigation operations through waters China claims control over.

Since US President Donald Trump took office however, his administration seems to have eased up on Beijing, turning down a Pentagon request to sail close to artificial islands China controls. It's been seen as another concession to China in the hopes of finding a solution over North Korea.

"I think if you're sitting in Beijing you have to be very pleased that Donald Trump is in the White House because he is ceding to China a great deal in terms of clout and advantage," Mike Chinoy, non-resident senior fellow at the University of Southern California's US China Institute, told CNN last week.

"In the meantime, countries in Asia that have not wanted a US-China clash but have wanted substantial American presence to counterbalance the growing clout of China ... are going to calculate that they can't count on the US in the way they did before."