Turkey police detained at least 25 people early on Wednesday in the western city of Izmir for tweeting 'misinformation,' state-run Anatolia news agency reported, as anti-government protests raged for a sixth day across the country.

They were still searching for at least a dozen others for their tweets which the police said contained "misleading and libellous information," according to the agency.

Ali Engin, a local official for the main opposition Republican People's Party (CHP), told Anatolia that the suspects were being held for "calling on people to protest".

He believed they would be released in the morning, he added.

"Have they already banned freedom of opinion and I have not heard about it?" tweeted one user, @CRustemov, as the news spread. "What on earth does it mean to get detained over Twitter!"

The crackdown comes after Turkish Prime Minister Recep Tayyip Erdogan scorned the protesters on Sunday.

Twitter was "trouble" and many users were spreading "unfathomable lies" on social media to stoke the protests against his government, he said.

Protesters, many of them young Turks, rely heavily on social media to organise demonstrations and warn each other of spots where police use tear gas and water cannon.

The wave of protests broke out on Friday after police tear-gassed demonstrators at a peaceful rally against plans to build on an Istanbul park.

The crackdown led to expressions of concern from Turkey's western allies, such as Britain and the United States.

Several thousand people have been detained since Friday, but most have already been released.

On Tuesday, Deputy Prime Minister Bulent Arinc apologised to those injured by police, while appealing for an end to the protests.