Beijing: In the realm of open-source intelligence, a primary method for Western experts to monitor China's military activities is by scrutinising photos of People's Liberation Army's new equipment shared online by amateur enthusiasts, CNN reported.

Posting images of military vessels or aircraft, often captured from outside PLA installations or through commercial flights near sensitive areas, has been a common practice as China rapidly modernises its forces. However, this activity faces a crackdown.

In a WeChat post titled "This is a cool hobby, but you must be very careful," China's Ministry of State Security said: "Some individual military enthusiasts severely endanger national military security by illegally obtaining information regarding national defence and disseminating them on the internet," CNN reported.

"With a focus on military airports, ports, national defence and military industrial units, they drove to or took ferries or planes that pass by designated routes, and clandestinely photographed with telephoto lenses or drones," said the post from the highly secretive civilian spy agency, as reported by CNN.

Repeat offenders could face imprisonment for up to seven years, while "first-time or occasional violators" might receive a warning. The Ministry of State Security oversees intelligence and counterintelligence activities both within China and overseas.

This warning aligns with China's increasing emphasis on national security across various sectors, particularly amid rising tensions with the United States. The Ministry of State Security recently launched a social media account to caution citizens about exposing China's secrets and urged them to join the fight against espionage.

The ministry's post specifically mentions the disclosure of operational and technical details of Chinese military hardware, with a focus on aircraft carriers. The construction progress of warships or aircraft can be revealed through images posted online.

China's newest aircraft carrier, the Fujian, has been a popular subject for amateur spotters as it undergoes outfitting at a Shanghai shipyard. The Fujian, weighing 80,000 tons and considered a rival to the newest US Navy carriers, is equipped with an advanced electromagnetic catapult system.

The warning underscores China's efforts to prevent the unauthorised sharing of sensitive military information, aligning with its broader strategy to control information flow and enhance national security.

Notably, the United States also has regulations restricting photography near certain military installations and equipment. The US Code prohibits making photographs or representations of vital military and naval installations or equipment without proper permission, and violators could face up to a year in prison.

While amateur military enthusiasts have been a common source of open-source intelligence, concerns about national security and protecting military secrets are leading both China and the United States to take measures against such activities, CNN reported.