A Chinese man has been sentenced to death for leaking more than 150,000 classified documents to an unidentified foreign power, state television said, offering unusual details of a kind of case rarely mentioned in public.

The man, a computer technician from Sichuan named as Huang Yu, worked for a government department which handled state secrets, but he was a bad employee and was sacked, the report said.

Filled with anger, he messaged a "foreign spy organisation" on the internet and offered to sell documents he had obtained while working for his former employer, who gladly took him up on his offer and so began their relationship, it added.

Meeting in Southeast Asia and Hong Kong, Huang eventually handed over 150,000 documents, covering secrets ranging from everything from the ruling Communist Party to military and financial issues, the report said.

But as he was no longer employed, he began to run out of documents to provide, and so targeted his wife and brother-in-law who also worked for government departments handling state secrets, state television said.

In the end, his frequent travel and sudden unexplained wealth caught up with him and in 2011 he was arrested, and then sentenced to death, it added.

The report did not say when or if the execution had happened, or where he was tried.

China's state secrets law is notoriously broad, covering everything from industry data to the exact birth dates of state leaders. Information can also be labelled a state secret retroactively.

President Xi Jinping has overseen a sweeping revamp of the security apparatus, aimed at combating threats both at home and abroad.