Turkish riot police using tear gas and water cannon battled protesters for control of Istanbul's Taksim Square.
The protests come hours after Prime Minister Tayyip Erdogan demanded an immediate end to 10 days of demonstrations.
Istanbul Governor Huseyin Avni Mutlu appeared on television, declaring that police operations would continue day and night until the square, focus of demonstrations against Mr Erdogan, was cleared.
Police fired volleys of tear gas canisters into a crowd of thousands of people in office clothes as well as youths in masks who had fought skirmishes throughout the day.
The crowds were scattered into side streets and nearby hotels.
Water cannon swept across the square targeting stone-throwers in masks.
The protesters accuse Mr Erdogan of overreaching his authority after 10 years in power and three election victories.
They thronged the steep narrow lanes that lead down to the Bosphorus waterway.
Many drifted gradually back into the square and lit bonfires, only to be scattered by more tear gas.
Governor Mutlu said 30 people had been injured.
Mr Erdogan had earlier called on protesters to stay out of Taksim, where a heavy-handed police crackdown on a rally against development of the small Gezi Park abutting the square triggered an unprecedented wave of protest.
Gezi Park has been turned into a ramshackle settlement of tents by leftists, environmentalists, liberals, students and professionals.
They see the development plan as symptomatic of overbearing government.
The protests, during which demonstrators used fireworks and petrol bombs, have posed a stark challenge to Mr Erdogan's authority and divided the country.
In an indication of the impact of the protests on investor confidence, the central bank said it would intervene if needed to support the Turkish lira.
Mr Erdogan, who denies accusations of authoritarian behaviour, declared he would not yield.
Western allies have expressed concern about the troubles in an important NATO ally bordering Syria, Iraq and Iran.
Washington has in the past held up Mr Erdogan's Turkey as an Islamic democracy that could be emulated elsewhere in the Middle East.
Victor in three consecutive elections, Mr Erdogan says the protests are engineered by vandals, terrorist elements and unnamed foreign forces.
His critics, who say conservative religious elements have won out over centrists in the AK party, accuse him of inflaming the crisis with unyielding talk.
The unrest has knocked investor confidence in a country long one of the world's best performing emerging markets.
Turkish lira is already suffering from wider market turmoil, fell to its weakest against its dollar/euro basket since October 2011.
The cost of insuring Turkish debt against default rose to its highest in ten months, although it remained far from crisis levels.