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To the tangle of emergency phone numbers in China — 110 for the police, 119 for fire, 120 for ambulance — add another: dial 12339 to report a spy.

The spy hotline made its debut in the northeastern province of Jilin on Sunday, according to a report in the state-controlled newspaper Jilin Daily, one year after the Chinese authorities introduced a new counterespionage law.

The hotline, run by the Jilin state security bureau, was set up to help citizens who encounter behavior that would harm China’s national security to report the matter immediately to state security organs, the Jilin Daily article said.

It warned of individuals or groups who “steal, pry out, buy or otherwise illegally obtain state secrets or intelligence, or conspire, coerce or pay government employees to become traitors.”

After repeated calls to the hotline on Monday, an officer finally picked up and answered a few basic questions about the service. He said the call, at 4:30 p.m., was the first of the day.

To report a spy, “tell us who he is, why you suspect him,” said the officer, who declined to give his name. “We’ll write everything down and report it to our supervisors. They will investigate the matter and get back to you.”

He said investigators would respond within a number of days, but that there was no reward.

A potential spy could be Chinese or foreign, and did not necessarily need to be an official. “Anyone can be a spy,” he said. “And anyone can also not be a spy.”

China does have a history, particularly during the Maoist era, of neighbors closely monitoring and reporting on each other. But before people rush to dial the spy hotline over the slightest suspicion, the authorities cautioned they weren’t looking for hearsay. The Jilin Daily warned that anyone responsible for “intentional fabrication, lies or false charges” would be punished.

Beijing has made it clear it considers espionage a grave threat. There have been several high-profile defections and attempted defections in recent years, and the National Security Agency appears to do extensive surveillance of Chinese mobile and Internet communications, according to disclosures by Edward J. Snowden, the former N.S.A. contractor.

In March, the government detained an American businesswoman who was traveling with a delegation in southern China. The woman, Phan Phan-Gillis, was formally arrested shortly before President Xi Jinping’s trip to Washington in September, for what a Ministry of Foreign Affairs spokesman called “suspicion of activities harmful to Chinese national security.”

In May, China detained two Japanese citizens on suspicion of espionage. And last year, Kevin Garratt and Julia Dawn Garratt, a Canadian couple who ran a coffee shop in Dandong, a town on the border with North Korea, were also detained, with the husband later formally suspected of stealing state secrets and the wife released on bail.

Meanwhile, a note circulating on Chinese social media sites gave more details of who might be a spy, including people with lots of money but unclear work titles, people who say controversial things and then observe quietly or instigate others. It listed as potential suspects workers at nongovernmental organizations, missionaries and journalists stationed abroad or writing on foreign affairs.

The note, which did not name its source, also listed people who work irregular hours, have studied in many countries or appear too old to study overseas, ask sensitive questions or “throw out reactionary phrases or exaggerate the advantages of foreign countries.”

There was no indication that the note came from an official source. Its content was similar to an unofficial guide on spotting foreign spies that circulated online a year ago.

Global Times, a newspaper run by the Communist Party, described the hotline as similar to a line set up by MI5, the British domestic intelligence agency, in the late 1990s. The F.B.I. also asks for people with nonemergency information about potential espionage or terrorism to contact its field offices.

A separate hotline for Hainan Province in southeastern China received dozens of calls after it was set up in July and led to the uncovering of more than 10 cases of alleged crimes, Legal Daily reported in September.

The hotline based in Jilin will be available for reports from across the country, Jilin Daily said.

Follow Austin Ramzy on Twitter @austinramzy.