Hundreds of police in riot gear forced through barricades in Istanbul's central Taksim Square today, pushing many of the protesters who had occupied it for more than a week into a nearby park.

Police briefly fired tear gas canisters and rubber bullets, prompting many of the protesters to flee the square into Gezi Park, where scores had been camping.

But there were running battles at one edge of the square between police and some groups of protesters, who threw fireworks, firebombs and stones at police water cannon.

Police made frequent announcements through loudspeakers, asking the group to stop attacking police and saying they did not want to use tear gas, before then firing the tear gas. A water cannon could be seen dousing another police vehicle that was set alight by a firebomb.

The police clampdown on Taksim Square came on the 12th day of nationwide protests.

They were sparked by a violent police crackdown on May 31 on a peaceful sit-in at a park in the square by people who were trying to prevent a redevelopment project that would replace the green space with a replica Ottoman Barracks.

The protests grew into wider demonstrations against what many see as prime minister Recep Tayyip Erdogan's increasingly authoritarian style of governing and his perceived attempts to impose a religious and conservative lifestyle in a country which has secular laws.

Mr Erdogan, a devout Muslim, says he is committed to Turkey's secular laws and denies charges of autocracy.

He has escalated tensions by vowing to press ahead with the Taksim redevelopment plans, dismissing the protesters as fringe extremists and the protests as undemocratic plots to topple his government, which was elected with 50% support.

He has called major pro-government rallies in Ankara and Istanbul this weekend to show that he too can get large numbers of his supporters out on the street.

Demonstrators had manned the barricades and prepared for a possible intervention when officers began massing in the area this morning.

Police took down large banners that had been hung by protesters on a building on the edge of the square.

They replaced them with a large Turkish flag and a banner with a picture of Mustafa Kemal Ataturk, the beloved founder of the secular republic 89 years ago after the collapse of the Ottoman Empire.

Huseyin Avni Mutlu, governor for Istanbul, said in a message issued on his Twitter account that the police operation was to dismount the banners hung on the building and at a monument on the square. He said people occupying the park at the square would not be touched.

As police clashed with activists near a side of the square where construction as part of the redevelopment plans has already started, bulldozers and rubbish trucks began cleaning up some of the barricades. A group of protesters was seen at another corner of the square, apparently trying to negotiate with police.

Some protesters were seen trying to build another small barricade on the square but were repelled by tear gas.

People coming off the metro in the middle of the square ran for cover. Protesters offered them antacid solution in bottles of spray to help protect them from the gas.

Hundreds of protesters remained inside Gezi park, some still sleeping in tents, some eating breakfast handed out by volunteers. Those affected by tear gas at Taksim were being helped to the medical station, with volunteers spraying milky white antacid solution on to their faces.

The gas later wafted into the park. People with only rudimentary protection, such as surgical masks, were choking and spluttering and others sprayed them with antacid.

One protester said he joined the protest in Gezi Park because his cousin was beaten by police during the initial clampdown that sparked the wider protests.

"I'm here because I'm trying to defend my human rights," said the protester, who identified himself as Kenan Agac. "I'm not against police but his morning they came and threw tear gas."

"If they had warned us, this wouldn't have happened. This was not necessary."

The Turkish government announced after a Cabinet meeting yesterday that Mr Erdogan would meet some of the peaceful Gezi Park protesters but authorities would not allow "illegal" demonstrations to continue.

A statement from Mr Mutlu's office said the banners of various groups taking part in the protests were making the square look as though it was under "occupation" and it was "negatively affecting our country's image in the eyes of the world opinion and leading to reaction from within the society".

One protester in the capital Ankara predicted that the police clampdown on Taksim would make the demonstrators more resolute.

"They chose not to listen to our youth," Onur Sivav said. "We will always show resistance when they attack us like today and this (protest) will spread all over the country."

Before the police action, the protests appeared to be on the wane, with the smallest number of demonstrators in the past 12 days gathering in Taksim last night. The protesters occupying Gezi Park had remained.

Smaller protests occurred in Ankara, with about 5,000 people demonstrating. Police there have used water cannon and tear gas to break up demonstrations almost every night.

Three people have died and more than 5,000 have been treated for injuries or the effects of gas during the protests. The government says 600 police officers have also been injured.