Flight MH066 was "diverted to Hong Kong due to an inoperative aircraft generator which supplies normal electrical power" on the Airbus A330-300, the airline said in a statement.
"However, electrical power continued to be supplied by the Auxiliary Power Unit," the company said, giving no further details on the equipment problem.
It said the aircraft landed in Hong Kong "uneventfully" and that all 271 passengers had been transferred to other carriers.
A Hong Kong Airport Authority spokeswoman said the aircraft touched down without incident at about 3:00 am.
The plane had departed from Kuala Lumpur at 11:37 pm (1537 GMT) on Sunday and was scheduled to arrive at Seoul's Incheon airport at 6:50 am, South Korean time.
AFP