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Flight HX640 departed from Hong Kong International Airport at around 9.30am and was scheduled to land in Fukuoka at 1.55pm (local time), according to plane-tracking website Flightradar24.
But three hours into the journey and after flying past the eastern coast of Taiwan, the flight made a U-turn and landed in Taipei at around 1pm.
It was not immediately clear how many people were on board, but according to Flightradar24, the aircraft model for HX640 is an Airbus A330-300, with a passenger capacity of 292.
A passenger later told local media an announcement was made on board at around 11.30am about the suspected fuel leak and the diversion.
After landing, passengers were told to remain on board while the aircraft was being checked and repaired, but more than two hours later they were told to disembark with their belongings, he said.