The Philippine authorities are investigating reports that China's coast guard shot at a Filipino fishing boat in disputed waters in the South China Sea.
This comes as Defence Secretary Delfin Lorenzana announced yesterday that construction works to transform Thitu, the largest island in the South China Sea that the Philippines occupies, into a tourist resort and marine research hub are set to begin in the coming weeks.
This is unlikely to sit well with Beijing, which has itself built a sprawling island with a 3km airstrip and anti-air defence systems on Subi reef, just 24km from Thitu.
A statement from the Philippine coast guard said men on a Chinese speedboat fired seven times upon the crew of the Princess Johann, 3.7km off the Chinese side of Union Reefs, a large atoll in the Spratlys.
"The crew hid and eventually cut their anchor line and fled the area," the coast guard said.
Mr Lorenzana said yesterday: "We still have to get the accounts of the fishermen. Right now, all we're getting is hearsay."
China's Foreign Ministry spokesman Lu Kang also said yesterday "it is unclear who was responsible".
But he added that China was "willing to work with the Philippines to deal with any maritime-related issues, to create a conducive environment for the healthy development of our bilateral relations".
If confirmed, the incident would be the first hostile episode in nearly a year involving the Philippines and China, which have seen warming relations since President Rodrigo Duterte was elected last year.
The Philippine Daily Inquirer reported the two planes carrying Mr Lorenzana and top military officials to Thitu yesterday were warned by China to stay away from its territories, a challenge Mr Lorenzana downplayed as normal protocol.
China claims most of the South China Sea and, in recent years, has been building up disputed reefs into islands that can house military facilities. Brunei, Malaysia, Taiwan and Vietnam also claim the Spratlys either wholly or in part.
Mr Duterte has sought to improve his nation's relations with Beijing by adopting a non-confrontational approach over their competing claims. China has responded by allowing Filipinos to fish in waters around Scarborough Shoal, another outcrop in the South China Sea that Beijing seized in 2012 after a stand-off with the Philippine Navy.
Responding to the Thitu visit, Chinese spokesman Lu Kang said Beijing "has lodged a protest with the Philippines".
Union Reefs is 230km from the Philippine coast. China has built islands on three of the reefs there - Johnson South, Gaven and Hughes.
The Philippine boat apparently sailed near one of these islands.
Union Reefs lies west of Mischief Reef, which China has also transformed into an island fortress.
• With additional reporting by Chong Koh Ping