Two Hong Kong journalists have been jailed in China for running an "illegal business" that sent political magazines to the mainland, one of their lawyers said Tuesday, as Beijing cracks down on press freedoms in the semi-autonomous territory.

Publisher Wang Jianmin, 62, was jailed for five years and three months and editor-in-chief Guo Zhongxiao was given two years and three months by the court in Shenzhen, Wang's lawyer told AFP.

"The two both admitted guilt to the court and said they 'will not appeal'," said Chen Nansha.

The sentences come after five booksellers from Hong Kong whose publishing house was known for gossipy titles about Chinese political leaders went missing and resurfaced in the mainland last year.

One of the five is still detained and another, who skipped bail and returned to Hong Kong, has revealed how he was blindfolded and interrogated for months during his detention.

Wang and Guo's magazines are widely available in the former British colony, which has greater freedoms than the mainland under agreements signed with Britain during the 1997 handover.

The pair were detained in June 2014, when Shenzhen police said they were "operating an illegal publication".

According to reports at the time of their trial in November, prosecutors said their Hong Kong-registered company National Affairs Limited had earned HK$7 million (US$900,000) from publications New Way Monthly and Multiple Face.

But the defence insisted that only eight copies were sent to the mainland, all to friends of the publisher, the South China Morning Post said.

Concerns are mounting about press freedoms in Hong Kong, where mass rallies in 2014 for fully free leadership elections failed to win political reform, and young campaigners are increasingly demanding more distance from Beijing.

Although the city has the status of a special administrative region of China, the two have separate legal systems, distinct police jurisdictions and maintain strict border controls.

Pro-democracy Hong Kong lawmaker Lee Cheuk-yan told AFP that the sentences imposed on the journalists were "a warning to anyone who wants to do business in China especially in the area of publication -- they will be subjected to suppression and censorship and if they are not following the party line, then they will be jailed".

Hong Kong's companies register shows that National Affairs Limited is a private firm registered in March 2007. Neither Wang nor Guo are listed as directors.

Willy Lam, a China expert at the Chinese University of Hong Kong, said the magazines -- which covered Chinese politics -- were printed in Hong Kong, then distributed in the mainland through unofficial networks.

"Beijing is sending an additional warning apart from the arrest of the Causeway Bay booksellers, not to play with fire," he said.