Indonesian fishermen have discovered a suspected Chinese submarine drone in waters considered strategically important to Australia.

The UUV was recovered from the water by a local fisherman on December 20, but was only reported to authorities six days later.

Security experts say the high-tech unpowered surveillance drone is known as a glider and relies on variable-buoyancy propulsion.

One official told the ABC the discovery is noteworthy because the UUV was seized in the middle of a crucial maritime route linking the South China Sea to Australia's northernmost city of Darwin.

According to Indonesian media, the captured drone is 225cm in length, with a 50cm wingspan and a 93cm-long trailing antenna.

It was initially handed to police, but has now been seized by the military and transferred to the 6th Main Naval Base in Makassar, where it is currently being inspected.

A prominent Indonesian-based security analyst who publishes under the online moniker of "Jatosint" claims the equipment is "very similar to China's 'Sea Wing' UUV, which, if it's true, [raises] many questions, especially how it managed to be found deep inside our territory".

Defence publication Naval News has noted the UUV gathers crucial oceanographic data including temperature, turbidity, salinity, chlorophyll and oxygen levels.

"This data may sound innocuous and it is often used for scientific research, but it can also be extremely valuable to naval planners, especially supporting submarine operations," Naval News reported.

In March last year, a similar Sea Wing UUV was found by an Indonesian fisherman near the Riau Islands, while another submarine drone was discovered at the beginning of this year near the Surabaya Naval Base.

In 2016, China protested after it seized a similar US Navy glider in international waters in the South China Sea, but the drone was only returned after the incident escalated.

Earlier this year, the ABC revealed a high-tech Chinese research vessel had been detected mapping strategically important waters off the Western Australian coast, where submarines are known to regularly visit.