HONG KONG (AFP) - Police charged at protesters gathered at a barricade in Mong Kok early Sunday, leaving many requiring medical treatment just hours after the government confirmed talks aimed at ending three weeks of pro-democracy rallies.

Police in heavy riot gear rained blows on protesters in the northern district of Mongkok, with some carried off on stretchers and others treated for head wounds, fractures and bruising, according to AFP journalists and medics at the scene.

Police said in a statement on Sunday that they had used "minimum force" as protesters approached their cordon lines. The police said the protesters had attempted to charge at cordon lines by pulling aside barriers and shoving officers.

Accusations that the police are being used as a political tool have dogged the highly respected force, which has a reputation across Asia for honest and impartial policing.

Hong Kong's government had confirmed on Saturday that it will open talks with student demonstrators on Tuesday, speaking before the fourth night of violent clashes in areas of the city paralysed by mass pro-democracy rallies.

"Right now we are planning that it will take place on the afternoon of Tuesday, October 21," Leung's deputy Carrie Lam told reporters on Saturday.

Lam said the talks - which will be broadcast live - would be focused on constitutional reform, with both sides allowed to bring five members to the meeting.

But hopes of any breakthrough are slim, with the government unlikely to cede to protesters' core demands - the resignation of embattled Chief Executive Leung Chun Ying and free leadership elections for the semi-autonomous Chinese city in 2017.

Beijing insists that candidates for the vote must be vetted by a committee expected to be loyal to China, and Leung has warned that the country's communist authorities have no intention of backing down.

- Uptick in violence -

Sunday's violence was indicative of a wider trend of increased force being deployed in the last few days as officers attempt to clear roads blockaded at three sites after two weeks of relative calm.

One volunteer medic said that she had seen four people with head injuries with "serious bleeding" as well as a fractured back. Another protester had collapsed unconscious with exhaustion, she said.

"One of the men with a head injury had been hit by a police baton three times," said Carla Chau, 20, a medical student volunteering at the first aid station set up at the Mongkok site.

Some injured protesters were taken to nearby Kwung Wah hospital, where activists told AFP at least 10 or more were being treated for injuries to their legs, arms and heads, including suspected fractures.

One protester said that police had reacted when a front-line of demonstrators blocking a key road opened their umbrellas and rested them on the barricades.

"They hit us without any reason when we were standing behind the roadblock. I was hit by a police stick four or five times. I protected myself with my hands and they hit my body... there was blood all over my head and they took me for medical treatment," said Jackie, 30, sitting with his head bandaged and blood still on his t-shirt.

"We didn't do anything - some people behind me opened out their umbrellas and then the police started hitting people. There was no aggressive action on our side."

Police have previously defended their actions as restrained in the face of increasingly hardcore protesters determined to reoccupy areas of the city the force has attempted to clear.

But video footage emerged showing plainclothes officers beating a handcuffed protester as he lay on the ground on Wednesday, just over a fortnight after riot officers fired teargas for the first time in years at crowds of largely peaceful demonstrators.

Over the weekend, pepper spray was used on protesters who retook ground that police had cleared for traffic.

The demonstrators have held sit-ins at three key intersections since Sept 28, causing major disruption in an Asian financial hub usually known for its stability.

- No common ground -

Many residents have become increasingly frustrated over the disruption caused by the protests, with road blockages causing heavy traffic jams in the city of seven million, and local companies complaining of a downturn in business.

The crowds of protesters have shrunk dramatically from their peak of tens of thousands earlier in the month.

A former British colony, Hong Kong was handed back to Chinese rule in 1997 under a "one country, two systems" deal that guarantees freedoms not seen on the mainland, including freedom of speech and the right to protest.

But fears have been growing that these liberties are being eroded, while anger has also soared over perceived political interference from Beijing and increasing inequality in the freewheeling financial hub.

The mass rallies are one of the biggest challenges to Beijing's authority since the Tiananmen pro-democracy protests of 1989.