At least 50,000 people took part in a protest by Turkey's main opposition CHP on Sunday ahead of a key court hearing that could oust the party's leadership, organizers and correspondents said.

The protesters packed Tandogan Square in Ankara in a massive show of defiance on the eve of the hearing in the Turkish capital.

CHP vice president Murat Bakan said there were 50,000 people and correspondents confirmed that many tens of thousands packed the square, waving Turkish flags and wearing T-shirts of the Turkish republic's founding father, Mustafa Kemal Ataturk.

In a speech, CHP leader Ozgur Ozel said the crowd had gathered to "stand against the [judicial] coup" being waged against the party, referring to yesterday's court hearing that could see him ousted as leader.

"This government does not want democracy. They know they cannot win the elections if there is democracy. They don't want justice: They know if there's justice they won't be able to cover up their crimes," he said.

"This case is political, the allegations are slander," he added. "This is a coup [and] we will resist."

"We are facing the grave consequences of Turkey's government abandoning the 'democracy train' and choosing to govern through oppression rather than the ballot box," Ozel told the crowd.Yesterday's hearing would seek to overturn the results of a CHP congress in November 2023, alleging vote-rigging. The congress elected Ozel as leader.

Critics say the case is a politically motivated attempt to undermine Turkey's oldest political party, which won a huge victory over Turkish President Recep Tayyip Erdogan's AKP in local elections last year and has been rising in polls.

Addressing the Turkish leader, Ozel said: "Erdogan, did you ever see Tandogan Square like this?"