But things began to change in 2013, as Beijing embarked on a programme of island-building and infrastructure development to transform the cluster of tiny islets and reefs into a centre for maritime research and, to the concern of several of its neighbours, a base for its military.

“I was shocked when I saw pictures of civilian aircraft landing on Fiery Cross Reef [in 2016], which was just a tiny rock emerging from the sea when I’d visited it a few years earlier,” Zhang said.

“It’s incredible how they turned it into a huge land mass with a 3,000-metre airstrip.”

In the years since those first flights, the development of the Spratlys has continued apace. Neighbouring Mischief and Subi reefs also now have airstrips capable of accommodating large aircraft, while dotted about the rocky chain are lighthouses, hospitals, weather observation stations and radar systems. There is also an array of buildings and facilities suitable for either military or civilian use, and several – like hangars for fighter jets – with a less ambiguous purpose.

It is the presence of the latter that has caused the most unease among rival claimants to the various land formations – and their associated fishing and resource exploration rights – scattered across the South China Sea.

Likewise, the United States and many of its European allies have criticised what they see as China’s increasingly aggressive moves in the region.

But Zhang, who since leaving the maritime safety administration in 2017 has worked as a researcher at the National Institute for South China Sea Studies, said it was not always like that.

In his more than 30 years at the agency, the 63-year-old said he was involved in scores of collaborative research projects with scientists from across the region, as well as many life-saving search and rescue missions.

“We built up a comprehensive communication mechanism and worked together to save countless numbers of people,” he said.

“It didn’t matter if they were Chinese or Korean or Vietnamese, or whatever. In the eyes of rescuers, lives matter, not where they come from.”

Although Beijing has repeatedly said that its island-building programme is for the global good, benefiting not only passing merchant ships but also fishermen from across Southeast Asia, many observers are less than convinced.

“What has happened in recent years has been very telling,” said Zhang Mingliang, an associate professor specialising in South China Sea studies at Jinan University in Guangzhou.

“Except the lighthouses, use of all the other public services that were offered by China has been very limited, while the number of stand-offs between Chinese fishermen and their rivals from neighbouring countries has been steadily rising.”

“These disputes and stand-offs are the result of an outdated concept by which many Chinese regard the resources of the South China Sea as an exclusive benefit that shouldn’t be shared,” Zhang said.

“But the more sustainable option is for China, as the largest and most powerful country in the region, to share those resources, and in doing so help to maintain long-term peace and stability.”

Professor Rommel Banlaoi, president of the Philippine Society for Intelligence and Security Studies, agreed that China should be more open to other countries.

“The South China Sea is a common area and claimants should be able to share its resources to benefit their people,” he said.

“But this requires cooperation and joint development by all parties, without prejudice to their respective claims.”

“Chinese and Filipino fishermen have already started working together in some areas, which is a good start,” she said.

“In the future, maybe Chinese shipbuilders can pass on some of their knowledge to help the Philippines build bigger and better fishing boats.”

Such a goal might still be some way off, however. Last month, the National Development and Reform Commission – China’s top economic planning agency – said that resource exploration would continue to be a key element of the country’s economic development plans as it sought to become a great maritime power.

“There is only about one take-off and landing each week,” he said. “And the main users are military transport planes carrying supplies to the islands or people back and to from the mainland.”