South Korea's President Yoon free, trials continue

South Korean President Yoon Suk Yeol walked out of a detention centre in Seoul on Saturday after prosecutors decided not to appeal a court decision to cancel the impeached leader's arrest warrant on insurrection charges.

Yoon, 64, remains suspended from his duties, and his criminal and impeachment trials continue over his short-lived imposition of martial law on December 3.

The Seoul Central District Court cancelled Yoon's arrest warrant on Friday, citing the timing of his indictment and "questions about the legality" of the investigation process.

"I would like to thank the Central District Court for their courage and determination in correcting the illegality," Yoon said in a statement.

As he left the facility, a relaxed and smiling Yoon, in a dark suit with no necktie and his hair showing some grey, stepped out of his car, waved, raised his first and bowed to cheering supporters waving South Korean and US flags.

His lawyers said the court decision "confirmed that the president's detainment was problematic in both procedural and substantive aspects," calling the ruling the "beginning of a journey to restore rule of law".

Prosecutors could not immediately be reached for comment.

The main opposition Democratic Party criticised prosecutors' decision for "throwing the country and people into crisis", and urged the Constitutional Court to remove Yoon from office as soon as possible.

In his impeachment trial, the Constitutional Court is expected to decide in coming days whether to reinstate or remove Yoon.

On Saturday, some 55,000 Yoon supporters rallied in Seoul's main districts, while 32,500 people demonstrated against him near the Constitutional Court, Yonhap news agency reported, citing unofficial police estimates.

The public, however remains largely anti-Yoon, with 60 per cent of respondents saying he should be removed from office and 35 per cent opposing removal, according to a Gallup Korea poll on Friday.

Before the prosecutors' decision, hundreds of Yoon supporters also protested in front of the Supreme Prosecutors' Office.

Yoon, the first South Korean president to be arrested while in office, has been in custody since January 15.