Il Nuovo Postiglione - Vast crowds rally in Istanbul in support of arrested mayor

The demonstrations, which began in Istanbul on Wednesday, have since spread to more than 55 of Turkey's 81 provinces, sparking clashes with riot police in the country's worst street protests in more than a decade.

Imamoglu's arrest came just days before he was to have been formally named as the main opposition CHP's candidate in the 2028 presidential race.

"Dictators are cowards!" and "AKP (Turkey's ruling party), you will not silence us!" read some of the placards in the Istanbul protest Saturday night, which appeared bigger and denser than the previous night's.

On the fringes of the rally, protesters once again clashed with riot police, who fired tear gas, rubber bullets and pepper spray and also used percussion grenades, AFP correspondents said.

In the capital Ankara, riot police used water cannon to push back protesters, while in the western coastal city of Izmir police blocked a student march headed towards the local AKP offices.

CHP leader Ozgur Ozel, addressing the massed protesters in Istanbul, told them they numbered "more than half a million".

He vowed the mobilisation would "defend" Ekrem and march on the courthouse where the mayor had been taken late Saturday.

At that courthouse, some 10 kilometres (six miles) away from the City Hall demonstration, police had set up a tight security cordon while around 1,000 protesters stood nearby shouting slogans.

Earlier Saturday, the 53-year-old mayor denounced the accusations against him as "immoral and baseless" in a statement released by City Hall.

"This process has not only harmed Turkey's international reputation but has also shattered the public's sense of justice and trust in the economy," he said.

- Turkish lira slides -

News of the mayor's arrest badly hurt the lira and caused chaos on Turkey's financial markets with the benchmark BIST 100 index closing Friday nearly 8.0 percent lower.

"We are here today to stand up for the candidate we voted for," 30-year-old Aykut Cenk told AFP outside the court, holding a Turkish flag.

"Just as people took the streets to stand up for Erdogan after the July 15 (2016) coup, we are now taking to the streets for Imamoglu," Cenk said.

"We are not the enemy of the state, but what is happening is unlawful."

The unrest has spread rapidly despite a protest ban in Turkey's three largest cities and a warning from Erdogan that the authorities would not tolerate "street terror".

"For four days, they have been doing everything they can to disturb the peace and divide our people," Erdogan said on Saturday.

"The days when politics and justice are guided by street terror are totally in the past," he added.

Earlier in the evening, Istanbul Governor Davut Gul said the authorities would not allow anyone to enter or leave the city who was "likely to participate in illegal activities".

Police have arrested 343 people since the start of the protests, the interior ministry said on Friday.

- Journalists 'targeted' -

Turkey's Journalists Union claimed the police had "deliberately targeted" journalists, saying many had been "severely beaten, shot with rubber bullets and had equipment broken".

Reporters without Borders (RSF) also denounced the "heavy-handed and completely arbitrary" violence against journalists, demanding those responsible be "severely punished".

Despite Imamoglu's detention, the CHP has vowed to press ahead with its primary on Sunday at which it would formally nominate him as the party's presidential candidate.

Observers said the government would likely seek to block the vote.

T.Barbieri--INP