South Korean prosecutors will question President Park Geun-hye over a burgeoning political corruption scandal engulfing her presidency.

It will be the first time a sitting South Korean president will be interviewed by prosecutors over a criminal case.

"It is correct, we are planning to question the president, but the date is undecided," an unnamed official at the prosecutors' office told Reuters news agency on Sunday.

South Korea: Mass rally calls for President Park's removal

"We need to question the president Tuesday - or Wednesday at the latest," Yonhap News Agency also quoted an official with the Seoul prosecutors' office as saying.

The official added they had sent a notice to her office and were waiting for a response.

Hundreds of thousands marched in the capital of Seoul on Saturday demanding Park resign, saying she was unfit to rule.

Public support for her has dropped to the lowest point ever, 5 percent, for a democratically elected South Korean leader.

The scandal centres on Park's shadowy confidant, Choi Soon-sil, who is accused of using her ties with the president to strong-arm local firms into donating millions of dollars to two non-profit foundations used by Choi for personal gain.

Prosecutors are investigating whether Park exerted improper pressure on company bosses to raise funds for the two foundations, Yonhap reported.

Bosses questioned

Prosecutors have already interviewed the de facto head of Samsung Group, Jay Y Lee, and the chairmen of Hyundai Motor Group and Hanjin Group over the scandal.

Park's office said it would be Tuesday at the earliest before it will have a position on the prosecutors' plan and was considering retaining a lawyer for the president.

South Korea: Seoul rally urges Park Geun-hye to resign

While some previous South Korean presidents have been mired in scandals or allegations of wrongdoing involving family members during their terms, none were directly questioned by prosecutors while they were in office.

Under South Korean law, a sitting president has immunity from prosecution except in cases of treason, but many scholars say a president can still face investigation.

Park has 15 months left in her term. If she steps down before the end of it, an election must be held within 60 days.

Inside Story - Will South Korea's president be forced out of office?

Source: Agencies