Police and firefighters investigate the site where a man set himself on fire near the Corruption Investigation Office for High-ranking Officials headquarters in Gwacheon, Gyeonggi Province, Wednesday. Yonhap

A man was seriously injured Wednesday after setting himself on fire near the investigators' office where impeached President Yoon Suk Yeol was being questioned over his short-lived imposition of martial law, police said.

The man, who has yet to be identified, set fire to himself in a grassy area near the Corruption Investigation Office for High-ranking Officials (CIO) in Gwacheon, Gyeonggi Province, at around 8:05 p.m., according to the police.

He was taken to a hospital and remained in serious condition.

Yoon has been undergoing questioning at the CIO office since the morning after being detained at his residence and brought there. (Yonhap)