Turkish riot police have stormed a central Istanbul park  firing tear gas and water cannon to evict hundreds of anti-government protesters hours after an ultimatum from Prime Minister Tayyip Erdogan.

Lines of police backed by armoured vehicles sealed off Taksim Square in the centre of the city as officers stormed the adjoining Gezi Park, where protesters had been camped in a ramshackle settlement of tents for more than two weeks.

Residents in surrounding neighbourhoods took to their balconies or leant out of windows banging pots and pans, while car drivers sounded their horns in support of the protesters.

Several people were brought out of the park on stretchers as ambulances waited to receive them.

Erdogan had warned hours earlier that security forces would clear the square if the protesters did not withdraw before a ruling party rally in Istanbul tomorrow.

"We have our Istanbul rally tomorrow. I say it clearly: Taksim Square must be evacuated, otherwise this country's security forces know how to evacuate it," he told tens of thousands of flag-waving supporters at a rally in Ankara.

A police crackdown on peaceful campaigners in Gezi Park two weeks ago provoked an unprecedented wave of protest against Erdogan, drawing in secularists, nationalists, professionals, trade unionists and students who took to the streets in protest at what they see as his autocratic style.

The unrest, in which police fired teargas and water cannon at stone-throwing protesters night after night in cities including Istanbul and Ankara, left four people dead and about 5,000 injured, according to the Turkish Medical Association.

The protesters, who oppose government plans to build a replica Ottoman-era barracks on Gezi Park, had defied repeated calls to leave.