Hong Kong protesters cut down a smart lamppost and police officers fired tear gas on Saturday as chaotic scenes returned to the protests for the first time in more than a week.

Key points: Demonstrators fear the high-tech posts could be equipped with facial-recognition software and used by Chinese authorities for surveillance

Demonstrators fear the high-tech posts could be equipped with facial-recognition software and used by Chinese authorities for surveillance Hong Kong's Government says smart lampposts only collect data on traffic, weather and air quality

Hong Kong's Government says smart lampposts only collect data on traffic, weather and air quality Police fired tear gas at protestors, who threw bricks and petrol bombs at officers

Protesters used an electric saw to slice through the bottom of the lamppost, while others pulled ropes tied around it.

The demonstrators, who were holding up umbrellas to hide their identities, cheered as it toppled over.

They were part of a larger group marching to demand the removal of the lampposts over worries they could contain high-tech cameras and facial recognition software used for surveillance by Chinese authorities.

The government in Hong Kong, which has been convulsed by more than two months of sometimes violent protests, said smart lampposts only collect data on traffic, weather and air quality.

The semiautonomous Chinese city has said it plans to install about 400 of the smart lampposts in four urban districts, starting with 50 in the Kwun Tong and Kowloon Bay districts that were the scene of Saturday's protest march.

"Hong Kong people's private information is already being extradited to China," organizer Ventus Lau said ahead of the procession.

"We have to be very concerned."

Police fired tear gas for the first time in more than a week after black-clad protesters set up makeshift barricades on a road outside a police station.

Demonstrators used an electric saw to cut the post before pulling it down with rope. ( ABC News: Brant Cumming )

Officers used minimum force to disperse the protesters after repeated warnings "went futile", the government said in a statement.

Protesters threw bricks and petrol bombs as police chased them down a main road.

The protest march had started peacefully as supporters chanted slogans calling for the government to answer the movement's demands.

The protests began in June with calls to drop an extradition bill that would have allowed Hong Kong residents to be sent to China to stand trial, and widened to include free elections for the city's top leader and an independent inquiry into alleged police brutality.

Hong Kong's government-owned subway system operator, MTR Corp, shut down stations and suspended train services near the protest route, after attacks by Chinese state media accusing it of helping protesters flee in previous protests.

MTR said Friday that it may close stations near protests under high risk or emergency situations.

Demonstrators feared the lampposts could be used for surveillance by Chinese authorities. ( ABC News: Brant Cumming )

The company has until now kept stations open and trains running even when there have been chaotic skirmishes between protesters and police.

Mr Lau said MTR was working with the government to "suppress freedom of expression".

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Earlier on Saturday, Chinese police said they released an employee at the British Consulate in Hong Kong as scheduled after 15 days of administrative detention.

Simon Cheng Man-kit was detained for violating mainland Chinese law and "confessed to his illegal acts", the public security bureau in Luohu, Shenzhen, said on its Weibo microblog account, without providing further details.

The Chinese Government has said Mr Cheng, who went missing after travelling by train to mainland China for a business trip, was held for violating public order regulations in Shenzhen, in a case that further stoked tensions in Hong Kong, a former British colony.

The British Government confirmed his release.

"We welcome the release of Simon Cheng and are delighted that he can be reunited with his family," the Foreign and Commonwealth Office said in a statement, adding that Mr Cheng and his family had requested privacy.

Mr Cheng, a Scottish Government trade and investment officer, was a local employee without a diplomatic passport.

The Global Times, a Communist Party-owned nationalistic tabloid, said on Thursday he was detained for "soliciting prostitutes".

China often uses public order charges against political targets and has sometimes used the accusation of soliciting prostitution.

Sunday's protest was the largest rally in the financial hub since the initial June 16 march. ( AP: Vincent Yu )

AP