Image copyright EPA Image caption President Park bows said she felt a "sense of shame"

South Korean prosecutors are set to question President Park Geun-hye over allegations of political corruption in a scandal that has engulfed her presidency.

Officials say this will be the first time a sitting president has been questioned by prosecutors.

Ms Park is accused of allowing her friend, Choi Soon-sil, to manipulate power from behind the scenes.

Hundreds of thousands rallied on Saturday to demand her resignation.

South Korean news agency Yonhap quoted officials as saying Ms Park's questioning should take place no later than Wednesday.

Prosecutors have also questioned top bosses at Samsung, Hyundai and Korean Air.

Lee Jae-Yong, vice chairman of Samsung Electronics, was questioned over whether Ms Park pressured the company into donating millions to foundations controlled by her friend Ms Choi.

Ms Choi is accused of trying to extort huge sums of money from South Korean companies and is under arrest on charges of fraud and abuse of power.

She is suspected of using her friendship with Ms Park to solicit business donations for a non-profit fund she controlled.

The president, whose approval ratings have plummeted to 5% because of the scandal, has said she is "heartbroken".

On Saturday, organisers said some one million people encircled the presidential compound in the South Korean capital of Seoul, in the largest anti-government rally the country has seen.

It was the latest in weeks of demonstrations against Ms Park.

Image copyright AFP Image caption Some one million protesters marched on Seoul

On Sunday, the presidential office said Ms Park was "earnestly considering ways to normalise state affairs" and that she had "heard the voices of the people at the rally".

She apologised earlier in November for putting "too much faith in a personal relationship".

"Sad thoughts trouble my sleep at night. I realise that whatever I do, it will be difficult to mend the hearts of the people, and then I feel a sense of shame.'"

She said wrongdoing would be punished, and that she was prepared to be investigated by prosecutors.

South Korea's constitution does not allow a sitting president to be prosecuted, but investigations are permissible.

Ms Park has 15 months left in her term. If she steps down elections must be held within 60 days.