SEOUL (AFP) - Pressure mounted on South Korean President Park Geun Hye on Saturday (Oct 29) ahead of a large-scale protest over revelations that she allowed a personal friend, with no government position, to meddle in affairs of state.

The scandal involving Ms Park's long-time confidante Choi Soon Sil has rocked her presidency, thanks largely to a lurid back-story involving talk of religious cults, shamanist rituals and corruption.

Thousands of people were expected to turn out for a mass, candle-lit rally later on Saturday in central Seoul to call on Ms Park, whose popularity ratings have plunged to record lows, to step down.

Ms Choi is being investigated for using her ties to Ms Park to coerce money out of major conglomerates, but the real shock was revelations that Ms Park had allowed Ms Choi to vet her presidential speeches and apparently advise her on crucial policy choices.

Ms Park has publicly apologised and late on Friday she told 10 of her senior advisers to tender their resignations ahead of a reshuffle of her presidential office.

Ms Choi, 60, is the daughter of shadowy religious figure Choi Tae Min, who headed a cult-like religious group and was a long-time mentor to Ms Park up until his death in 1994.

Media reports have portrayed Ms Choi as a Rasputin-like figure with an inappropriate and unhealthy influence over Ms Park that she inherited from her father.

Ms Choi left the country for Germany in early September as reports of her alleged influence-peddling began to emerge.

An early banner displayed at the venue for Saturday's rally read "Choi come back, Park get out".

Ms Choi's lawyer said she was well aware of the "gravity" of the situation and was "willing to return home to be questioned and punished if she did anything wrong".

Prosecutors have taken in two of Ms Choi's close aides for questioning, including one who told reporters that Ms Choi had been behaving as Ms Park's de facto regent.