Protesters in Hong Kong have reoccupied the Mong Kok site, a key zone in the heart of the city, after police had cleared the area on Friday, sparking some of the most violent confrontations since the demonstrations began three weeks ago.

On Saturday, police used batons and pepper spray against protesters who were shielding themselves with umbrellas on the central district, but were forced into a partial retreat as the sun began to rise, to cheers from the crowd.

Hong Kong police said in a statement that they had made 26 arrests in scuffles with a crowd that had swelled to 9,000 people in the early hours, with 15 officers sustaining injuries in the clashes.

The police have lost control of the situation. They've lost their minds Protester in Hong Kong's Mong kok

Activists rushed to rebuild makeshift barricades in an area police had opened to traffic 24 hours earlier, while thousands of others staged a sit-in at the protest camp that has existed for nearly three weeks, AFP news agency reported.

"The police have lost control of the situation. They've lost their minds," said protester Peter Yuen.

"We've come here peacefully, to peacefully protest for our future."

Earlier on Friday, officers had significantly reduced the size of the northern Mong Kok camp, the second largest after the main protest site opposite the government's headquarters in central Hong Kong, in a swift dawn raid that saw no resistance from demonstrators.

Throughout Friday, demonstrators managed to hold on to one side of a multi-lane road where the camp had been located. Police then struggled to maintain order as crowds of pro-democracy supporters began to swell during the evening.

The Asian financial hub has been rocked for weeks by demonstrations, drawing tens of thousands of the city's residents, calling for fully free elections and the resignation of the city's leader Leung Chun-ying.

Protesters have held sit-ins at three major intersections causing significant disruption to a city usually known for its stability, and presenting Beijing with one of the most significant challenges to its authority since the 1989 Tiananmen protests.

China has insisted that whoever stands to replace Leung in 2017 elections must be vetted by a committee that is expected to be loyal to Beijing, a proposal protesters have dismissed as "fake democracy".

ANALYSIS BY OUR REPORTER

Barricades are once again coming up in Mong Kok. Protesters now say their site is bigger than the original police cleared on Friday morning.

But in contrast to the skirmishes and clashes on Friday night, Saturday has so far been uneventful. Coming up to midnight, there was a larger police presence.

Student leaders addressed crowds in Admiralty. Most people were subdued as they listened to the various speakers, who said they welcomed upcoming talks with the government.

They said that in the discussions they will ask Chief Secretary Carrie Lam and the executive for a solution to working towards democracy.

In other words, they seem ready to listen to what the government has to say. But they have made it clear that they will not be giving up any more of their protest areas.

The government has meanwhile said the talks will be held at a neutral location, but the mediator they are proposing is a university professor with strong ties to the chief executive and is known as being pro-Beijing.

Already that gives the sense that the discussion will be skewed in the government's favour.