By Katy Wong

HONG KONG (Reuters) - A Hong Kong court found seven police officers guilty on Tuesday of beating a handcuffed pro-democracy activist during demonstrations in 2014, a rare incident of police brutality in the financial hub that triggered public outrage.

The 79 days of student-led protests paralyzed parts of Hong Kong and posed one of the greatest challenges to the central government in Beijing in decades.

But Beijing gave no grounds on demands for greater democracy and resentment among some residents of the city, which enjoys a significant degree of autonomy, has simmered ever since.

The trial centered on an incident on Oct. 15, 2014, at the height of the protests.

A group of police officers was filmed dragging a protester, Ken Tsang, to a dark corner by a pumping substation next to the protest site, where he was kicked and punched. The officers were later suspended from duty.

District court judge David Dufton said in a written summary that all seven officers were "guilty of assault occasioning actual bodily harm", but were found not guilty of the more serious charge of causing grievous bodily harm.

"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.

Tsang, a social worker, suffered face, neck and shoulder injuries. He was handcuffed with plastic zip ties at the time, though the court heard he had earlier thrown some liquid at police.

Two senior officers among the seven convicted had not taken part in the assault directly, Dufton said, but should have been duty-bound "to prevent the commission of a crime, even by fellow police officers." Instead they had encouraged the others to carry out "unlawful personal violence" on Tsang, he added.

The seven men, who had pleaded not guilty, appeared in suits and ties and showed no emotion when the verdict was read. Several of Tsang's supporters cheered in the public gallery.

Outside the court, Tsang's supporters were heckled by a group of about 70 people who chanted "support our police".

The court did not give a date for sentencing. Under Hong Kong law, they could be jailed for up to three years.

Heavy-handed policing is rare in Hong Kong and the case triggered public outrage and deepened tension during the protests in which clashes occasionally erupted.

Tsang told Reuters he needed to consider the verdict before making a statement.

Hong Kong reverted from British to Chinese rule in 1997 under a "one country, two systems" formula that accords the city a degree of autonomy and freedom not enjoyed in mainland China.

China bristles at dissent, however, especially over issues such as demands for universal suffrage.

Many in Hong Kong are increasingly concerned about what they see as Beijing's meddling in city affairs. Unease about the city's future has stoked protests and has even led to calls for independence from China.

(Writing by James Pomfret; Editing by Robert Birsel)