Thousands of people have rallied in Seoul, demanding the resignation of South Korean President Park Geun-hye.
The protest comes after Ms Park ordered 10 of her senior advisers to quit after admitting she had allowed an old friend to edit political speeches.
Choi Soon-sil, who holds no government job, is also suspected of meddling in policy-making and exploiting her links with the president for financial gain.
On Saturday, prosecutors raided the homes of several presidential aides.
They seized computers and files belonging to the officials who are suspected of being Ms Choi's accomplices.
'Lost her authority'
Police said about 8,000 protesters took to the streets on Saturday evening. Organisers said some 20,000 people turned out.
Many held posters reading "Step down, Park Geun-hye".
"Park has lost her authority as president and showed she doesn't have the basic qualities to govern a country," opposition politician Jae-myung Lee was quoted as saying by the Associated Press news agency.
Ms Park's televised apology over the scandal last week failed to defuse the situation, only sparking widespread accusations of mismanagement.
The scandal has badly eroded her popularity before next year's elections, with some opposition parties calling on her to resign.
Ms Park, 64, became the first woman to lead South Korea after winning presidential elections in 2012. She has proposed that presidents be allowed to stand for a second consecutive term.
Ms Choi is the daughter of shadowy religious cult leader Choi Tae-min, who was Ms Park's mentor until his death in 1994.
Ms Choi, who left the country last month and is currently in Germany, has denied benefiting financially from her government links.
Her lawyer said she was well aware of the "gravity" of the situation and was willing to return to South Korea if summoned by prosecutors.