North Korea is facing what could be its most serious defection in years after a man who managed funds for the ousted uncle of leader Kim Jong-un fled the isolated country, South Korean media said on Friday.

The aide has sought asylum in South Korea and is currently being protected by South Korean officials in a secret location in China, cable news network YTN said, citing a source familiar with the matter.

YTN said the man managed funds for Jang Song Thaek, whose marriage to Kim's aunt and proximity to the young leader made him one of the most powerful men in North Korea.

But Jang was relieved of his posts last month, according to South Korea's National Intelligence Service (NIS), and YTN said the sacking could have followed the aide's defection.