Police put the number at 155,000.

So far the candlelight protests have been largely peaceful, with many families participating, but there was still a heavy police presence, with buses and trucks blocking access roads to the presidential Blue House.

“We want to have a peaceful protest,” said Nam Jeong-su, spokesman for the Korean Confederation of Trade Unions.

Nam said he expected the ranks of protesters to be swelled by thousands of students who sat the national college entrance exam earlier in the week.

And this being South Korea – with the world’s highest smartphone penetration rate – many had downloaded a special app showing a burning candle to hold aloft during the rally.

Hours before Saturday’s protest was scheduled to start, a crowd of around 50,000 had already gathered along Seoul’s ceremonial Gwanghwamun boulevard, south of the presidential Blue House.

“We’re here to show my children the site where history is being made”, said Kim Myung-hee, 30, who came with her husband and two daughters.

“Park simply doesn’t feel ashamed of the wrongs she and her friend did. She must go”, Kim said.

Prosecutors said they would formally indict Choi and two other alleged accomplices on Monday, prior to trial.

They have been investigating allegations that Choi, 60, leveraged her relationship with Park to coerce donations from large companies like Samsung to non-profit foundations which she set up and used for personal gain.

She is also accused of interfering in government affairs, despite holding no official position.

Lurid reports of the unhealthy influence Choi wielded over Park have seen the president’s approval ratings plunge to 5 per cent – a record low for a sitting president.

Fresh from the college entrance exam they spent their entire school lives preparing for, a large number of high-school students were among the early arrivals at Saturday’s rally.

“Making this country better is more important than entering a good college”, said Park Chai-un, as he collected donations to buy candles and bottled water for protesters.

“When things go this wrong with the country, it will become even more difficult for us to find jobs. That’s why I am here,” said one of his classmates, Kim Mi-sung.

In an effort to soothe public anger, Park has agreed to relinquish some of her extensive presidential powers and submit to a probe by an independent special prosecutor to be appointed by parliament.

But she has offered no sign of resigning and some members of her ruling Saenuri Party have started to push back at the popular protests of the past month.

“Candles are candles. They will just go out with a gust of wind,” one Saenuri lawmaker said.

The scandal has paralysed the Park administration and caused the president to pull out of a gathering of Asia-Pacific Economic Cooperation (APEC) leaders in Peru next week.

But after a lengthy hiatus, Park has visibly returned to normal duties and announced she will attend an annual summit with China and Japan in Tokyo next month.

The presidential Blue House said Park was receiving baskets of flowers from supporters, and organisers of a pro-Park rally near Gwanghwamun said they expected 5,000 people to turn out.

Police said they would keep the two rallies well separated to prevent any clashes.