Demonstrators gathered overnight on Ankara’s main shopping thoroughfare, Tunali.
Among their demands is the sacking of police chiefs who oversaw a fierce crackdown on days of protest against the perceived authoritarian nature of Turkey’s government.
But unrest broke out as the police fired pepper spray and smoke grenades to disperse the crowds.
In retaliation, protesters set fire to the makeshift barricades they have built around the square.
The police doused them with water.
Prime Minister Recep Tayyip Erdogan returns to Turkey later on Thursday from a visit to North Africa.
He faces demands that he apologise over the fierce police crackdown on demonstrators.
To date, two people have died in the week-long protests and more than 4,000 have been injured.