Press freedom further declined in Hong Kong in 2015, driven by growing self-censorship and government interference as Beijing expands its influence over the city's boisterous media, a new report said Saturday.

The southern Chinese city prides itself on having relative freedom of expression compared with severely restricted reporting in mainland China, a legacy of Britain's handover of power in 1997.

"Press freedom in China, Hong Kong and Macau deteriorated further in 2015, as the Communist Party of China used every means at its disposal to control the media," the International Federation of Journalists' China Press Freedom Report said.

The report comes at a time when the fate of five booksellers, feared to have been detained in mainland China after disappearing late last year have put residents on edge with concerns the semi-autonomous city's freedoms are being eroded.

The five are from Hong Kong's Mighty Current publishing house, known for salacious titles critical of Beijing leaders.

"There has been strong outcry from the Hong Kong people, with many concerned about their personal safety and freedom of speech," the report said of sentiment after the disappearances.

The report also predicted China's ruling Communist Party will use resources to strengthen its influence in the city, which will hold elections for its legislature later in the year and for a new leader in 2017.

"As Hong Kong goes to elections next year the party is also using its considerable wealth to consolidate its influence over the region," it said.

Last year's report warned of "intervention behind the scenes" at a time when tensions remained high after more than two months of mass protests for fully free leadership elections in late 2014.

Ken Tsang, a pro-democracy activist who was allegedly beaten by police during the protests in an attack captured by television cameras and beamed around the world said the situation in Hong Kong was "terrible".

"Maybe we can say we have lots of freedoms but somebody is threating you at your back, I think all Hong Kong citizens can feel that," Tsang told AFP after a court hearing on Thursday.

"The situation is not that good, we are terrified," he said.

A British colony until 1997, Hong Kong is ruled under a "one country, two systems" deal that allows it far greater civil liberties than those enjoyed on the Chinese mainland, including freedom of speech and the right to protest.

The report, presented at Hong Kong's Foreign Correspondents' Club, also called the outlook in 2016 for the rest of mainland China "even worse".

Chinese authorities have detained and harassed reporters, used forced television confessions and other methods in limiting and influencing reporting, the report said.