MANILA (Reuters) - Philippine and Vietnamese navies have been playing soccer, volleyball and tug-of-war games together on a South China Sea island, the latest get-together by two countries concerned by Chinese assertiveness in the disputed waters.

The two sides played in mixed teams on Thursday on Southwest Cay in the Spratly archipelago, the Philippine navy said, the third event of its kind since 2014 on an island held four decades ago by the Philippines, but now under Vietnamese control.

The games are among a series of exchanges between two countries, quietly demonstrating their unity in the face of Beijing’s expanding presence and signs of militarization of manmade islands in the Spratly chain.

Ariesh Climacosa of the Philippine Naval Forces West said the games showed how the two sides could get along and would trust and understand each other better.

Relations strengthened under the previous Philippine administration, leading to the signing of a strategic partnership in 2015, at a time when both countries were locked in fierce disputes with China and enjoying warm ties with the United States.

But ties have since become more uncertain, due largely to Philippine President Rodrigo Duterte’s decision to charm rather than confront Beijing, while also turning more hostile toward Washington.