President Park Geun-hye's lawyer has said prosecutors investigating a corruption scandal engulfing the leader, her aides and acquaintances can question her next week, according to reports.

Park retained Yoo Young-ha as her lawyer on Tuesday after the prosecutors investigating a favours scandal said they would try to question her this week, making her the first sitting leader to be questioned in a criminal case.

The lawyer’s statement, reported by South Korea's state-run Yonhap news agency, comes as Park's approval ratings have plunged, after hundreds of thousands of protesters took to Seoul's streets last week demanding her resignation.

South Korea: Prosecutors to question President Park

The scandal centres on Park's shadowy confidante Choi Soon-sil, who is accused of using her ties with the president to coerce local firms to donate millions of dollars to non-profit foundations that Choi then used for personal gain.

Choi, 60, is also accused of interfering in state affairs to the extent of nominating officials and editing Park's speeches, even though she has no official title or security clearance.

Yoo said Park was willing to "cooperate" in the investigation but said she needed more time.

"I will rush through my preparations and cooperate so that an investigation into the president can be conducted next week," Yoo said in a text message sent to reporters.

Under South Korea's constitution, the incumbent president may not be charged with a criminal offence except insurrection or treason.

However, many have argued that the sitting president can be investigated by prosecutors and then charged after leaving office.

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

Choi, whose father was an elusive religious figure and a long-time mentor to Park until his death in 1994, was arrested earlier this month for abuse of power and fraud. Two presidential aides have also been arrested.

Prosecutors on Thursday also requested a local court to issue an arrest warrant for a former vice sports minister in connection with the case, Yonhap said.

Kim Chong, who served as vice sports minister for three years until last month, is accused of helping Choi's foundations win lucrative state contracts.

Source: Agencies