What began as a peaceful protest aimed at preserving an Istanbul park, became an ugly battlefield scarred with tear gas, glass bottles and water canons.
Hundreds of people had slept overnight in the park as part of Occupy Gezi, to challenge the bulldozing of the green space to make way for new flats and a shopping mall.
Activists say they could not have predicted the police reaction. Photos posted on social media appear to show protesters being forced to disperse by water canon.
Amnesty International said it was concerned by what it described as "the use of excessive force" by the police against what had started out as a peaceful protest.
Reuters reported that primary school children on a school trip were caught up in the tear gas.
"We do not have a government, we have Tayyip Erdogan...Even AK Party supporters are saying they have lost their mind, they are not listening to us," said Koray Caliskan, a political scientist at Bosphorus University who attended the protest told the news agency. "This is the beginning of a summer of discontent."
Many received severe injuries, including an 34-year-old Egyptian female tourist who remains in a critical condition after suffering a brain haemorrhage which she was hit by a police gas canister.
Twelve have been hospitalised for trauma injuries and hundreds suffered tear gas side effects.
Sirri Süreyya Önder, an MP from the Kurdish BDP party, was taken to hospital after he was reportedly hit in the shoulder by a tear gas cartridge, the Guardian reported.