Political activist Joshua Wong looks on ahead of his verdict over an anti-China protest, at the Eastern Law Courts Building in Hong Kong on June 7, 2016. Picture: Anthony Wallace/ AFP

Hong Kong - Hong Kong student leader Joshua Wong was acquitted on Tuesday over an anti-China protest in the first of a raft of cases against him to reach a verdict.

Wong, 19, was the teenage face of the pro-democracy Umbrella Movement, which brought parts of Hong Kong to a standstill for more than two months in 2014 with street rallies calling for fully free leadership elections.

His acquittal comes as tensions remain high in the semi-autonomous city with fears growing that Beijing is tightening its grip.

“The result of this trial proves that it was a political prosecution,” Wong said in brief comments after the verdict.

The teen was in court over a small protest in June 2014 - ahead of the mass rallies - which saw dozens gather outside Beijing's representative office in the city.

The protesters were opposing a “white paper” from China that asserted its control over Hong Kong, and the burned a reproduction of the document.

Wong, student leader Nathan Law, and activists Raphael Wong and Albert Chan were all charged with obstructing police, which carries a possible two-year jail term.

The four pleaded not guilty and all were acquitted at magistrates' court on Tuesday.

Around 20 supporters gathered outside court before the verdict carrying yellow umbrellas - the symbol of the pro-democracy movement.

“We will not bow our heads to the Chinese authorities,” said Law, before going into court.

Separately, Wong recently stood trial over a demonstration that saw students climb into the Hong Kong government complex on September 26, 2014, triggering wider rallies that exploded two days later when police fired tear gas to disperse crowds.

That verdict will be given later this month.

The university student also faces another charge relating to a protest in Mong Kok, where the most violent clashes happened during the pro-democracy rallies.

Hong Kong is semi-autonomous after being returned to China by Britain in 1997, with much greater freedoms than seen on the mainland.

But there are fears those freedoms are being eroded by increasing interference from Beijing.

Wong and Law were also detained last month after running onto a major Hong Kong highway in a bid to stop the motorcade of senior Beijing official Zhang Dejiang.

They were released on bail.