The Police Union in Hong Kong was "shocked" at a court's verdict against seven police officers charged of assaulting a pro-democracy protester in 2014.

The policemen were each sentenced to two years in prison on 17 February. Representing around 20,000 officers, the police union said in a statement the verdict was "unacceptable".

"I feel shocked like every one of you and found it unacceptable. The jail term already went beyond our acceptance level," the chairman of the junior police officers' association, Joe Chan Cho-kwong, wrote in a statement to union members on 17 February, quoted in the South China Morning Post.

The statement continued: "It is understood that the seven colleagues have decided to appeal against the case that bears a lot of suspicions and an unacceptable sentence. We will raise funds for them so as to ease their financial difficulties brought by the incident."

District court judge David Dufton found the officers guilty of assault occasioning actual bodily harm, which carries a sentence of up to three years. The officers were cleared of the more serious charge of grievous bodily harm.

The policemen were arrested in November 2014 on suspicion of assaulting Ken Tsang, a social worker, during a confrontation at a protester camp in Hong Kong a month earlier.

"The court was satisfied that by carrying Tsang to the substation where he was dumped on the ground and immediately assaulted, the only inference to draw was that Tsang was carried ... to be assaulted," Dufton wrote in a summary of the verdict.

The officers were suspended from the force after video footage emerged of them assaulting Tsang who was handcuffed with plastic zip ties.

In footage broadcast by television network TVB, plain-clothed officers were seen shoving the pro-democracy activist and kicking him on the ground.

After being released from custody, Tsang appeared at a news conference showing evidence of the beating, including a bump on his head, a black eye and bruises across his chest and back.

The judge noted that while two of the officers did not take part in the beating, they forfeited their duty "to prevent the commission of a crime, even by fellow police officers". They had, he said, instead encouraged the other policemen to carry out "unlawful personal violence".

The ruling was received with mixed reactions. Several of Tsang's supporters cheered in the public gallery, but outside the court, they were heckled by a group of about 70 people who chanted "support our police", Reuters reported.

The police brutality stoked tensions that were already high because of clashes between pro-democracy demonstrators and police. The authorities were cracking down on the student-led demonstrations, dubbed the Umbrella movement protests, which saw much of downtown Hong Kong brought to a standstill for 79 days. Protesters were demanding more independence from China which regained control of the former British territory in 1997.

Hong Kong was granted a degree of freedom and autonomy not enjoyed by the rest of mainland China under the "one country, two systems" style of governance agreed by the UK and China in negotiations on the handover.

But concern continues to grow in Hong Kong over what is seen as increased meddling by Beijing in internal affairs. Five Hong Kong booksellers were arrested by the Chinese authorities last year but critics say the authorities abducted them. Billionaire businessman Xiao Jianhua, who disappeared in late January, was reportedly snatched by Chinese police and is believed to be in police custody on the mainland.