Protesters wearing cut-out of South Korean President Park Geun-hye (C) and Choi Soon-sil attend a protest denouncing President Park Geun-hye over a recent influence-peddling scandal in central Seoul, South Korea, October 27, 2016. [Photo/Agencies]

SEOUL -- Calls are mounting for a criminal investigation into South Korean President Park Geun-hye over a scandal surrounding Choi Soon-sil, the president's longtime confidante suspected of peddling undue influence and pulling strings behind the scenes.

Park's approval rating dropped to 10.9 percent, according to a local pollster Realmeter survey announced on Thursday. It is based on a poll of 1,518 adults conducted from Monday to Wednesday.

Daily support for Park kept falling from 13.4 percent on Monday to 11.1 percent on Tuesday and 10.2 percent on Wednesday each as public views spread that the 60-year-old private citizen's intervention in state affairs could not happen without the president's protection and connivance.

Most shocking was Park's approval rating among those in their 20s that posted 1.6 percent. Support among those in their 30s and 40s tumbled to 3.1 percent and 7.7 percent respectively.

Park's political home turf of South Gyeongsang province recorded 8.6 percent in support for Park, lower than the nationwide average. The number in another support base of North Gyeongsang province stood merely at 14.2 percent.

Amidst the sagging support, demand is increasingly stronger that President Park be investigated by prosecutors over her involvement in the Choi Soon-sil scandal that put the first South Korean female leader in the biggest political crisis.

South Korean Justice Minister Kim Hyun-woong told lawmakers that he would recommend an investigation into President Park after reviewing its necessity and possibility if it is necessary for getting down to bedrock in accordance with the development of the ongoing prosecutors' probe into the scandal.

Kim said that if President Park volunteers for it, there would be no limitation to the investigation though he noted that a majority of law experts claim no legal ground for search and seizure toward the president theoretically.

Under the country's constitution, a president cannot be criminally indicted during his or her presidency except for treason charges. Some of law experts say the president can be investigated on condition that the criminal prosecution is suspended by the end of presidency.

Reversing his Oct. 27 remarks that President Park cannot become a subject of criminal investigation, the justice minister opened the door for a probe into the president amid escalating public furor over the behind-the-curtain big shot.

Kim Byong-joon, the prime minister nominee, told reporters on Thursday that it would be possible for the president to be investigated though there are different interpretations of the constitution, saying all the people are equal under the law.

Kim, who worked as senior presidential policy secretary under the 2003-2007 Roh Moo-hyun administration, was appointed as new prime minister on Wednesday.

Opposition parties have opposed to the appointment as President Park tapped him as the country's No.2 executive post without any prior notice to or consultations with the parliament.

Scores of ruling Saenuri Party lawmakers, members of non-President Park faction within the party, have called on all of the party leadership to voluntarily resign to take responsibility for the political crisis.

Public support for the main opposition Minjoo Party increased to 33.5 percent this week from 29.6 percent tallied on Oct. 24. The rating for Saenuri Party tumbled from 29.2 percent to 20.7 percent in the same period.