Foreign espionage agencies have conducted a series of intelligence-gathering and technological activities to spy on China's maritime areas in recent years, posing growing threats to national security, according to the Ministry of State Security.

In a statement released on its WeChat account on Wednesday, the ministry underscored the strategic importance of safeguarding marine data, warning that if such data is exploited by foreign agencies with malicious intent, it could seriously endanger China's national security.

Foreign intelligence agencies have used various means to conduct reconnaissance and surveillance operations in China's territorial waters, the ministry said.

In one case, authorities found that a marine public welfare organization, under the guise of providing data to relevant departments, had frequently established ocean monitoring stations along China's coastline from south to north, collecting marine monitoring data from strategically important areas of the sea.

Deploying covert espionage devices in China's territorial waters is a common tactic used by foreign agencies, the ministry said. Chinese fishermen once retrieved a new type of underwater espionage device deployed by a foreign country that was covertly collecting oceanographic data and monitoring nearby naval activities.

Foreign agencies may also secretly embed "backdoors" in China's marine observation sensors and operational equipment to steal sensitive data, the ministry said.

The statement lists various types of marine data that are crucial to safeguarding China's maritime rights and interests, including seafloor topography, marine meteorology, and remote sensing data.

Seafloor topography data, which include information on underwater mountains, trenches, basins, and other geomorphological features, are vital for studying marine geological structures and ocean dynamics.

It also serves as the basis for building coastal defense systems and deploying underwater military facilities, according to the ministry.

Weather and oceanographic data, including temperature, air pressure, waves and currents, have a direct impact on the planning and execution of military operations, the ministry added.

"Some may assume that most of the marine data is basic and nonsensitive, and therefore irrelevant to national security. But this is far from the truth," the ministry said. "These types of data may seem ordinary, but they have become a form of 'digital border defense' over the maritime territory."

"If any suspicious device is discovered, and personal safety can be ensured under appropriate conditions, it may be retrieved and securely stored. It should then be promptly handed over to national security authorities upon returning to port," the ministry said.