The protest at Gezi Park started late on Monday after developers tore up trees but widened into a broader demonstration against Prime Minister Tayyip Erdogan's Islamist-rooted Justice and Development Party (AKP).
Riot police recently clashed with tens of thousands of May Day protesters in Istanbul. There have also been protests against the government's stance on the conflict in neighbouring Syria, a recent tightening of restrictions on alcohol sales and warnings against public displays of affection.
Police staged a dawn raid on demonstrators who had been camping for days in Gezi Park in anger at plans to build a shopping mall, and clouds of tear gas rose around the area in Taksim Square that has long been a venue for political protest.
"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. "This is the beginning of a summer of discontent."
The Istanbul Medical Chamber, a doctors' association, said at least 100 people sustained minor injuries on Friday, some of them when a wall they were climbing collapsed as they tried to flee clouds of tear gas.
Transformation in Turkey
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.
Erdogan has overseen a transformation in Turkey during his decade in power, turning its economy from crisis-prone into Europe's fastest-growing. Per capita income has tripled in nominal terms since his party rose to power.
He remains by far Turkey's most popular politician, and is widely viewed as its most powerful leader since Mustafa Kemal Ataturk founded the modern secular republic on the ashes of the Ottoman Empire 90 years ago.
The unrest has not reached the levels of mass demonstrations seen in other parts of the Middle East or even parts of Europe in recent years, but it reflects growing concern about Erdogan's authoritarianism.
Hundreds of military officers have been jailed on charges of plotting a coup against Erdogan in recent years; others including academics, journalists and politicians face trial on similar accusations.
Erdogan has made no secret of his ambition to run for the presidency in elections next year when his term as prime minister ends, exacerbating opposition concerns.
"These people will not bow down to you" read one banner at the Gezi Park protest, alongside a cartoon of Erdogan wearing an Ottoman emperor's turban.
Postings on social media including Twitter, where "Occupy Gezi" – a reference to protests in New York and London last year – was a top-trending hashtag, and Facebook said similar demonstrations were planned for the next few days in other Turkish cities including Ankara, Izmir, Adana and Bursa.
"Kiss protests" – in which demonstrators are urged to lock lips – had already been planned for Istanbul and Ankara this weekend after subway officials were reported to have admonished a couple for kissing in public a week ago.
Erdogan is pushing ahead with a slew of multibillion-dollar projects which he sees as embodying Turkey's emergence as a major power. They include a shipping canal designed to rival Panama or Suez, a giant mosque and a third Istanbul airport billed to be one of the world's biggest.
Speaking just a few miles from Gezi Park at the launch on Wednesday of construction of a third bridge linking Istanbul's European and Asian shores, Erdogan vowed to pursue plans to redevelop Taksim Square.
Architects, leftist political parties, academics, city planners and others have long opposed the plans, saying they lacked consultation with civic groups and would remove one of central Istanbul's few green spaces. – Reuters