ISTANBUL: Turkish police stormed an Istanbul park on Saturday after protesters defied an ultimatum from Prime Minister Recep Tayyip Erdogan to end their occupation of the site, in a major escalation of more than two weeks of anti-government unrest.

Two hours after Erdogan warned of police intervention if protesters did not leave Gezi Park, the epicentre of nationwide protests, officers entered the green patch firing volleys of tear gas and jets of water.

Thousands of campers scrambled as police trampled tents, pulled down banners and broke down barricades in the park. A city cleaning crew then swiftly moved in to clear the site as darkness fell.

Earlier, police also used tear gas and bursts of water to disperse hundreds of demonstrators from Taksim Square, which borders Gezi Park.

The police action sent tensions soaring in the civil unrest in which four people have been killed and nearly 7,500 injured, and has posed the biggest challenge yet to the decade-long rule of Erdogan's Islamic-rooted government.

The 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 crackdown sparked an outpouring of anger, snowballing into countrywide demonstrations against Erdogan, seen as increasingly authoritarian.

Tensions boiled over on Saturday after demonstrators in Gezi Park refused to clear out in return for Erdogan's promise that he would suspend the site's controversial redevelopment.

Rebuffed, Erdogan issued a stark warning at an election rally attended by tens of thousands of supporters of his ruling Justice and Development Party (AKP) in the capital Ankara.

"We have an Istanbul rally tomorrow (Sunday)," the premier told cheering loyalists in a sea of red Turkish flags.

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