Beijing has ramped up espionage warnings in recent years as ties with the United States and other Western nations have cooled.

Its Ministry of State Security (MSS) said this month that foreign spooks were targeting public officials with tantalising "honey traps" and blackmail to infiltrate the country and steal sensitive information.

In another admonition on Thursday, the ministry turned its focus to newbie workers who, in its view, might be spending a little too much time online.

It cited the example of a young man surnamed Jiang, a "newly employed cadre at a certain agency" who received a confidential document during a regular work meeting.

"Out of a desire to show off, he took a photo of the front page and posted it on his WeChat Moments, causing a leak," the MSS said, referring to the social media app's news feed.

It added that Jiang faced punishment from the ruling Communist Party and "administrative discipline" for his actions.

In a similar case, a greenhorn worker surnamed Tian "casually" shared his progress on a confidential project with a colleague, whose family overheard the conversation and posted about it online.

Another "novice" mistake involved a scientific worker surnamed Li, who lazily uploaded sensitive data to an artificial intelligence app to generate a research report, causing a leak.

"New employees in confidential units... must strictly distinguish between work and life boundaries, strictly follow confidentiality agreements while socialising and entertaining, and strictly control their 'desire to show off' and 'vanity'," the MSS said.

Beijing and Washington have long traded accusations of espionage.

In China, spying can be punishable by death.

The MSS said in March it had handed such a sentence to a former engineer for leaking state secrets to a foreign power.

This month the MSS said it had cracked three spying plots, including one in which a public servant was bewitched by the "seductive beauty" of a foreign agent.

Enmeshed in a "meticulously designed honey trap", the hapless employee was blackmailed with "intimate photos" and forced to hand over official documents, landing him five years in prison, the ministry said.