South Korea's financial watchdog launched an investigation on Monday into the leak of personal information from South Korea's Hyundai Capital, the consumer finance unit of Hyundai Motor Group, a Financial Supervisory Service official said.

Hyundai Capital said personal information on about 420,000 of its 1.8 million customers was leaked when an unidentified hacker attacked its database.

The company said in a statement on Sunday it was conducting its own investigation into the incident, citing the possibility that passwords on some customer accounts may have also been compromised.

Hyundai Capital deals with auto financing, personal loans and home mortgages and is jointly owned by South Korea's largest automaker Hyundai Motor Co and GE Capital, which holds a 43 percent stake.

(Reporting by Ju-min Park; Editing by Jonathan Hopfner)