Semi-autonomous Hong Kong owes much of its success as a financial hub to its transparent legal system.

Unlike authoritarian China's judicial structure -- where opaque courts are party-controlled and convictions all but guaranteed -- Hong Kong's is internationally respected.

But as Beijing cracks down following last year's huge and often violent pro-democracy protests, judges are now finding themselves in the crossfire of the city's festering political divide.

Much of that criticism comes from a pro-establishment bloc infuriated by acquittals or perceived light sentences for protesters.

Ta Kung Pao and Wen Wei Po -- two staunchly pro-Beijing newspapers based in Hong Kong -- have led the charge, publishing articles calling for judicial reform and deriding "yellow judges" -- the colour associated with the democracy movement.

Prominent local pro-Beijing politicians have joined in, calling certain judges biased, and lobbying for the creation of a sentencing committee to impose harsher jail terms.

- 'Dog judge' -

In October, graffiti daubed in red paint appeared on a wall reading in Chinese: "Police arrested people but the 'dog judge' released them".

That message targeted former magistrate Stanley Ho, who had recently acquitted two people of assaulting police.

Ho slammed two testifying officers for "telling lies to cover lies", and said the force used against those they arrested was "completely unnecessary".

District councillor Jocelyn Chau, one of the two exonerated, remains furious about the trial and months spent on bail.

"The long wait, the pressure you face from family members and friends when you go through the trial, are unnecessary sufferings," she told AFP.

"Yet, the officers who lied face no consequences."

Testimony or evidence from police in at least 27 protest cases has been dismissed by magistrates as either unreliable, contradictory or not credible, and resulted in acquittal, according to an AFP tally based on local media reports.

No officer has been disciplined for evidence given on the stand. A police spokesperson said any court complaint about an officer would be handled "in a fair and impartial manner".

Of more than 10,000 people arrested at protests, about 2,300 cases have gone on to some form of judicial proceedings with 331 convictions, according to Hong Kong police statistics.

Charges have been withdrawn in another 42 cases, and 65 cases have ended in acquittal.

- 'Political pressure' -

Antony Dapiran, a Hong Kong lawyer and author of two books on the city's protest movements, said the acquittals show the courts are doing their job.

"These cases show both the political pressure that prosecutors must be under to bring every case to court... and the independence of Hong Kong's judiciary in continuing to throw these cases out," he told AFP.

"However, this will inevitably lead to more attacks on Hong Kong's independent judiciary from Beijing and its supporters," he added.

Pro-democracy supporters have also criticised some judgements and sentences, especially via social media comments, but no major opposition figure has called for overhauling the judiciary.

Last week, Hong Kong leader Carrie Lam criticised "unjustified attacks" against judges and called on people to respect court decisions "regardless of his or her political stance".

The judiciary has also taken to publishing several trial transcripts and judgements by magistrates accused of favouring protesters in a bid to show how decisions were reached.

Still, many of those exonerated by trial feel angry about their ordeals.

Lee Sheung-chun, who was acquitted of assaulting police, spent nearly a year under a bail curfew with his passport confiscated.

"The past year was unhappy, worrisome and nerve-wracking," the 32-year-old warehouse worker said.

His defence lawyers unearthed video that contradicted the police's story and a magistrate ruled the testimony of three officers in court was unreliable.

"There are lots of cases out there with no video. One should bear in mind that the burden of proof lies with the prosecution," Lee's lawyer Wong Ying-kei told AFP.

"We need to remind the judges and prosecution that cases where police give false testimony do exist. We need to hold them accountable."