SEOUL (AFP) - South Korea's embattled president was visited by "shadowy" doctors who injected her with human placenta extract, a parliamentary inquiry into a growing corruption scandal heard on Wednesday (Dec 13).

The ongoing, two-month hearing is seeking to get to the bottom of a scandal that triggered mass nationwide protests and led to lawmakers voting to impeach Park Geun Hye last Friday.

Park stands accused of colluding with her longtime friend Choi Soon Sil to strong arm donations from large companies worth tens of millions of dollars.

The scandal raised questions as to what extent the friend influenced the president's personal life, as it emerged that Park had sought treatment from doctors who were not part of her official medical staff but had ties with Choi.

The two doctors - who treated Choi for years - testified that they had visited Park at her residence multiple times, often without the presence or knowledge of the presidential medical team.

One of them said he had given Park a series of injections containing human placenta extracts and vitamins, widely used as an anti-ageing treatment or for detoxification in South Korea.

He later became a member of the presidential medical team.

The other doctor, who runs a plastic surgery clinic in the affluent Seoul district of Gangnam, testified that he had visited Park multiple times since 2013 to handle her "skin troubles."

He however denied that he had performed cosmetic procedures on Park as lawmakers grilled him with past photos of small bruises on the president's face, which he said were possibly traces of wrinkle filler needles.

A former chief of the presidential medical team told a TV station that he had turned down Park's request to inject human placenta extract due to doubts over its medical benefit, before he was dismissed in 2014.

"I heard rumours that some (doctors) were visiting the presidential Blue House in the evening...but did not take it seriously back then," he told lawmakers on Wednesday.

Details of the president's health conditions are state secrets.

"It is a very grave problem that doctors who were not named as part of the official medical team entered the (presidential) Blue House and had physical access to the president," one lawmaker said, describing them as "shadowy doctors".

Another lawmaker pointed out the pair had gone through minimal security checks when visiting Park repeatedly.

"Our head of state was left completely vulnerable...as the official presidential security protocol was ruined by her private relationship," he said.

Choi, daughter of a shady late religious figure who was also close to Park, is known to have wielded enormous power over Park from her daily wardrobe choice to nomination of top officials.

Choi is now awaiting trial on charges of fraud and abuse of power.