Hong Kong police swooped at dawn to clear a democracy protest site Friday, tearing down tents and barricades hours after the city's embattled leader reopened his offer of talks to end nearly three weeks of disruptive demonstrations.

Mongkok -- the second biggest protest site after the main Admiralty district -- has seen violent scuffles between demonstrators calling for full democracy in the southern Chinese city and pro-government groups.

The dawn raid, which was met with no resistance from demonstrators, comes as the city's Chief Executive Leung Chun-ying renewed his offer for talks with student protesters a week after abruptly pulling out.

"It happened really fast," said 20-year-old protester Prince Yung Chung-To. "A lot of police came at 5 o'clock shouting they were going to clear the area."

"There was no fighting, it was all peaceful," added another protester who did not wish to be named, gesturing at a couple of dozen demonstrators facing a line of riot police.

Police were seen tearing down tents, barricades and umbrellas -- the defining symbol of the democracy movement -- and piling them into the back of a van.

The Mongkok site is separate to the largest protest site outside government offices in the Admiralty district on the city's main island, where tens of thousands have intermittently rallied, and battled with police.

Protesters are demanding free leadership elections for the semi-autonomous city, but China insists that candidates for a 2017 vote must be vetted by a committee loyal to Beijing.

Ongoing sit-ins for nearly three weeks at three major intersections have caused major disruption in a city usually known for its stability.

Protesters have called Beijing's proposal a "fake democracy" and have vowed to remain on the streets until their demands are met, despite growing impatience among some Hong Kongers and attacks on their camps by pro-government thugs.

Soaring tension

City authorities pulled out of talks with student protesters last week, plunging the two sides deeper into an impasse that has no obvious ways out.

The offer of new talks came a day after video footage showing plainclothes police officers beating a handcuffed demonstrator sparked widespread anger.

Tensions have spiked in recent days as police began raiding protest sites and tearing down barricades near the government's besieged headquarters, with officers using pepper spray against crowds who angrily accused them of links to criminal triad gangs.

Police on Thursday said seven officers involved in the beating video were now suspended pending an investigation.

The incident has become another public relations disaster for the police, who were severely criticised for firing tear gas on umbrella-wielding protesters on September 28 in a move that attracted worldwide attention.

Amnesty International and the United States both called for a swift investigation of the officers.

Leung also refused Thursday to rule out further barricade clearances by police that led to the recent increase in clashes with protesters after two weeks of relative calm.

"We cannot allow the negative affect on Hong Kong to continue because of the blockage of these streets. Police will use appropriate methods at the appropriate time to handle this problem," he said.

At the protest camp in Hong Kong's busy Causeway Bay shopping district, protesters complained that police used a nearby fire on Thursday as a cover for removing more of the metal barriers they have used to block off the streets.

"We don't know if the fire that broke out was an accident or if it was on purpose, so we are worrying," said one 20-year-old protester who gave his name as Ryan.

Leung, who has kept a low profile throughout the last week, had been due to attend a question and answer session at the city's parliament but cancelled his appearance after "security and risk assessments".

He spoke to the media Thursday at his official residence which, unlike his office, is not surrounded by protesters.