A South Korean court extended the detention of impeached President Yoon Suk Yeol on Sunday over concerns he could destroy evidence linked to his martial law declaration, enraging his supporters who attacked the court building.

Hundreds of pro-Yoon protesters smashed windows and broke down doors to enter the court after the decision was announced, chanting the name of the president, who plunged South Korea into its worst political chaos in decades with his bid to suspend civilian rule.

The president's December 3 martial law declaration lasted just six hours, with lawmakers voting it down despite him ordering soldiers to storm parliament to stop them. He was impeached soon after and suspended from duties.

Yoon was detained in a dawn raid on Wednesday on insurrection charges after he refused investigators' summons and went to ground in his residence, using his presidential security detail to resist arrest.

South Korea's first sitting president to be detained, Yoon had also refused to cooperate during the initial 48 hours detectives were allowed to hold him.

The disgraced leader, who attended court for the first time on Saturday over his case, will now remain in custody, with the new warrant allowing investigators to keep him for up to 20 days.

Yoon's lawyer Seok Dong-hyeon slammed the court decision, but also warned the president's supporters not to escalate the situation.

"This is likely not what President Yoon desires," he said in a statement, adding violence could also "create burdens" for the president's future trials. (AFP)