China has sentenced a former computer technician to death for selling state secrets to foreign spies, the state media reported on Tuesday.

The convicted felon Huang Yu sold a cache of 150,000 classified documents (including military codes) from 2002 to 2011 to foreign spy agencies and pocketed $US700,000.

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Yu worked as a cryptographer in a research institute in Chengdu, a city in southwestern China, before he was arrested.

Huang's death sentence is the second case of a Chinese national receiving the capital punishment for espionage since 2008. Before him, the government had executed a science researcher and his relative who sold military secrets to Taiwan.

Secret information

National security experts said Huang sold a trove of secret information, including 90 top-secret documents, to foreign spy agencies. Huang's case is said to be one of the largest known leaks in China in recent years.

Chinese President Xi Jinping has rallied the public to help the government catch domestic and foreign spies, reminding the people that they will be amply rewarded when they coordinate with the police.

On Tuesday marked the National Security Education Day and to celebrate the occasion, Beijing has established an anti-spying hotline.

Counter-Espionage Law

President Xi has been on top of the security situation in Beijing after signing the counter-espionage law in 2014 which aims to arrest foreign spies and the Chinese nationals who assist them.

Analysts said although no reason has been given by the authorities about why Huang received the death penalty only recently, the publicity of his case was a glaring proof of Xi's tenacity to highlight the threats posed by spy agencies and the government's determination to protect the country's national security at all costs.

"The authorities are, in this way, advertising the fact that there is severe punishment available for crimes against national security," said Eva Pils, a legal scholar at King's College London.

Beijing has been tackling cases of espionage which have caught media attention in the recent years.

Chinese authorities are currently prosecuting a Canadian man and his wife, who ran a cafe near the border with North Korea, for spying and stealing state secrets.

Last year, Beijing detained four Japanese nationals on suspicion of espionage.  

TagsCounter-Espionage Law, Death Sentence, classified documents, Huang Yu, national security experts, top-secret documents, President Xi Jinping, National Security Education Day