President Tayyip Erdogan's opponents say they will repair the damage done to human rights during his rule, promising a new era for democracy and freedoms if he loses power.

With Erdogan facing his toughest test yet at the ballot box on Sunday, rights advocates hope his defeat will draw a line under an era they say has seen judicial independence eroded, freedom of speech curbed, and journalists and politicians jailed.

"If we take power, everyone will speak freely and be harshly criticised," Gokce Gokcen, deputy chairwoman of the opposition Republican People's Party (CHP), told Reuters.

"We will focus on building a pluralistic democracy.

"As we put an end to the autocratic rule in Turkey, we will take comprehensive measures so that no authoritarian regime will emerge again."

While Ankara defends its rights record, critics say civil liberties and freedoms have suffered major setbacks in the past decade as Erdogan has concentrated ever more power in his hands, prompting concern among Western allies.

Gokcen said an opposition-led government would introduce changes including a constitutional amendment to secure judicial independence and put an end to politically-motivated lawsuits.

Among other changes, she said an opposition-led Turkey would also respect rulings of the European Court of Human Rights, with which Erdogan has clashed, notably over the case of Osman Kavala.

A civil activist, Kavala was jailed for life in 2022 on a charge of trying to overthrow the government by financing protests.

Western powers see it as a politically-driven case.

The opposition has long said Erdogan and his AK Party influence the courts.

The government denies this.

Polls are showing a tight race between Erdogan and his main challenger, CHP leader Kemal Kilicdaroglu, candidate of a six-party alliance, who has a slight lead.

Seeking to rally his conservative base, Erdogan has declared the opposition "pro-LGBT" while on the campaign trail.

Rights activists say the LGBTQI community, often described as "deviant" by Erdogan, has been systematically targeted.

Supporters of Erdogan, who was once jailed for reciting a poem authorities said incited Islamist sedition, view him as a defender of democracy and civilian government who confronted the military to halt its interference in politics.

"Despite all provocations, we did not give up rule of law, democracy and legitimacy", Erdogan tweeted on Wednesday.

In campaign rallies, he has sought to remind voters of his early years in power when he lifted a ban on women wearing headscarves at university and in public sector jobs.

But critics say women's rights have suffered in recent years, notably in 2021 when the government pulled Turkey out of the Istanbul Convention, an international treaty combating gender-based violence, on grounds that it threatens family values and that local laws were sufficient.

The opposition plans to reverse the decision.

Human Rights Watch, in its World Report 2022, said Erdogan's government has set back Turkey's human rights record by decades.

Ruhat Sena Aksener of Amnesty International said the election was taking place in "a very dark picture of human rights", and that re-establishing the judiciary's independence and impartiality must be the next government's first priority.