Turkish police stormed an Istanbul park with tear gas and water cannon Saturday after Prime Minister Recep Tayyip Erdogan warned protesters to end their occupation of the site.

The crackdown came just two hours after Erdogan issued an ultimatum to protesters to leave Gezi Park, the epicentre of nationwide protests, ahead of a rally of his ruling party in the city on Sunday.

Thousands of startled campers scrambled to escape the clouds of acrid smoke, clearing the site within minutes and leaving only empty tents behind. A city cleaning crew and bulldozers swiftly moved in to clear the site.

The Taksim Solidarity group, seen as most representative of the protesters, condemned what it described as a "brutal attack".

"The police raid left hundreds of protesters injured and there are dozens more who were hit by rubber bullets," it said in a statement.

Istanbul governor Huseyin Avni Mutlu said 29 people were injured in Saturday's unrest, none seriously.

Shortly before dismantling the park, police armed with riot shields and wearing gas masks also fired salvos of tear gas and water to disperse hundreds of demonstrators from Taksim Square, which borders Gezi Park.

The police action, a major escalation of two weeks of conflict between the government and protesters, sent tensions soaring.

The recent civil unrest has so far claimed four lives and injured nearly 7,500 people across the country. It represents the biggest challenge yet to the decade-long rule of Erdogan's Islamic-rooted government.

As evening fell, many Gezi Park demonstrators sought refuge in nearby five-star hotels, while pockets of protesters continued to battle with police throughout the night.

Thousands also took to the streets in the capital Ankara and the western city of Izmir, but there were no reports of clashes.

Turkey's trouble first began when a peaceful sit-in to save Gezi Park's 600 trees from being razed in a redevelopment plan prompted a brutal police response on May 31.

The violence sparked an outpouring of anger, snowballing into countrywide demonstrations against Erdogan, who critics say is increasingly authoritarian.

Earlier on Saturday, the premier issued a stark warning to the Gezi Park holdouts.

"We have an Istanbul rally tomorrow (Sunday)," the premier told tens of thousands of supporters at an election rally for his ruling Justice and Development Party (AKP) in Ankara.

"Let me put it clearly: empty Taksim. If it is not evacuated, this country's security forces know how to evacuate there," he told cheering loyalists.

"Nobody can intimidate us," he added. "We don't take orders or instructions from anybody except from God."

-- 'This is not over' --

Mey Elbi, a 39-year-old yoga teacher, was in the park when police entered at around 9:30pm.

"They took our goggles and gas masks," she told AFP, referring to items the protesters carry against tear gas attacks.

"I won't give up," she vowed. "We're angry, this is not over. The world has seen that together, we can stand up to Tayyip."

After days of taking a combative stance against the demonstrators, dismissing them as "looters" and "extremists", Erdogan made an unexpected conciliatory gesture in late-night talks with protesters on Friday.

He agreed to abide by a court-ordered suspension of Gezi Park's redevelopment and said that if the court deemed the project legal, he would hold a referendum on plans to rebuild Ottoman-era military barracks on the site.

But the Taksim Solidarity group on Saturday rejected the proposals, vowing to "continue our resistance".

It said the government had failed to address their demands, which include a call for arrested demonstrators to be released and for police chiefs in cities that saw clashes to be sacked.

Erdogan felt "cheated" after protesters rejected his olive branch, AKP deputy Huseyin Celik said.

The United States and other Western allies have widely criticised Erdogan's handling of the crisis in recent weeks, undermining Turkey's image as a model of Islamic democracy.

Opponents have accused the premier of repressing critics and of forcing conservative Islamic policies on the mainly Muslim but staunchly secular nation -- including religious education reforms and restrictions on alcohol sales.

While opposition to him is intense, the 59-year-old, who has been in power since 2002, remains the country's most popular politician.

His AKP has won three elections in a row and took nearly half the vote in 2011, having presided over strong economic growth in the country of 76 million people.

The premier has insisted that this weekend's election rallies for local polls next year are not meant as a show of strength to protesters.

But as he gave his fiery speech in Ankara, he stood in front of a banner reading: "The game is over. It's time to write history".