Former President Park Geun-hye apologised to the nation after she left the presidential complex on Sunday, two days after the Constitutional Court upheld her impeachment.

Ending some four years' stay in the presidential mansion, Park headed back to her private residence in Samseong neighbourhood of southern Seoul, Yonhap news agency reported. 

In a statement read out by her former spokesman, she vowed to clarify the truth behind the corruption allegations that led to her ouster.

"I would like to express my apology for failing to fulfill my duty to the end," Park said. "Although it may take time, I believe the truth will eventually be revealed," she added.

Park was ferried to her private residence in a black limousine, chased by journalists on motorbikes. When she arrived, she waved to cheering supporters, smiling broadly, and shook hands with political allies.

Hundreds of supporters were waiting for her arrival at home, chanting "Park Geu-hye, the President!" and "Cancel the impeachment!" 

Pro-Park lawmakers from the Liberty Korea Party also greeted the former leader upon her arrival.

The Constitutional Court on Friday upheld Park's impeachment over a corruption scandal. 

But she had stayed on in the presidential complex while keeping silent on the ruling, prompting rivals to criticise her for behaving as if she won't accept the result.

As rumours of Park's possible early return spread in the afternoon, hundreds of her supporters gathered in front of the house, where she lived from 1990 to 2013 before moving into the presidential office.

Some 1,000-strong police force was deployed around the house to prevent possible violence.

Hwang Kyo-ahn, who is loyal to Park, is now the acting president.

The country's Election Commission said a "free and fair" vote will be held by May 9 at the latest.

The early frontrunner, human rights lawyer Moon Jae-in, of the Democratic Party, warned Park that she "must not destroy or take the national records outside" the presidential complex, also known as the Blue House.