A radio recording of a Royal Australian Air Force (RAAF) surveillance plane conducting a freedom-of-navigation flight over the South China Sea has emerged for the first time.

The audio has been published by the BBC following a reporting assignment in the disputed Spratly archipelago.

In the scratchy radio recording, an RAAF pilot is heard speaking to the Chinese Navy.

“China Navy, China Navy,” the voice says.

“We are an Australian aircraft exercising international freedom of navigation rights, in international airspace in accordance with the international civil aviation convention, and the United Nations Convention on the Law of the Sea – over.”

But the Chinese did not respond. The BBC said it recorded the flight audio from a RAAF AP-3C Orion surveillance aircraft in the early afternoon on November 25.

Australia has stepped up military surveillance flights over the South China Sea to give a signal to Beijing that it means to continue operating in the regional flashpoint area despite heightened tensions provoked by territorial disputes.

In a move that is likely to grate with the Chinese government, an RAAF P-3 Orion aircraft carried out patrols in the air space in recent weeks, prompting a demand from Chinese naval forces in the waters below to explain itself.

Defence confirmed the recent flight, though only after the plane’s presence happened to be noticed by a BBC journalist in the area, who recorded an Australian crewman telling the Chinese navy that the plane was “exercising international freedom of navigation rights”.

While such surveillance flights have been conducted for years in the South China Sea under Operation Gateway, their tempo has been increased in the past 12 to 18 months, it is understood.

This amounts to a calculated signal to Beijing that Australia does not accept the sea territory claims generated by China’s building of artificial islands in the area, which is subject to claims by Malaysia, the Philippines, Vietnam and others.

The government played down the patrol, saying it was a routine part of Operation Gateway

But experts said it sent a clear message that Australia would not yield space to China’s growing ambition to unilaterally control the strategically important waters.

Crucially, it comes amid heightened tensions after a US destroyer sailed close to one of China’s artificial islands in late October in a so-called “freedom of navigation” exercise.

– SMH, BBC