South Korean prosecutors have questioned the heads of some large conglomerates, including the chairman of Hyundai Motor, and plan to question the de factor head of Samsung Group SAGR.UL and others in a probe into a political scandal involving President Park Geun-hye, media reports said on Sunday.

Prosecutors are investigating whether Park exerted improper pressure on "chaebol" conglomerate bosses to raise funds for two foundations at the center of an influence-peddling scandal involving a friend of hers, Yonhap said citing prosecution sources.

Officials at the prosecutors office could not immediately be reached for confirmation or comment. A Hyundai Motor spokesman declined to comment and Samsung Group could not immediately confirm the report.

Park, whose public support rating has dropped to the lowest point ever for a democratically elected South Korean leader at 5 percent, is facing growing calls for her to step down.

Hundreds of thousands marched in the capital Seoul on Saturday demanding her resignation. Many of them said Park was unfit to rule.

Park faces allegations she allowed her friend Choi Soon-sil to use her closeness to the president to meddle in state affairs and wield influence in the sports and cultural communities.

Prosecutors are investigating people close to Park over whether they had pressured dozens of the country's biggest conglomerates to contribute to two foundations set up to support the cultural and sports communities.

Park has said she had discussed with conglomerate heads in July last year her desire for them to contribute more for culture without elaborating.

South Korean prosecutors raided Samsung Electronics last week as part of the probe over the scandal and whether the company separately gave millions of euros to a company controlled by Choi and her daughter.