TAIPEI - Taiwan's state-run power operator said on Thursday that electricity is in the process of being restored after a malfunction at a major power generation plant caused supply to be cut in the southern part of the island.

Taipower said there had been an incident with a transformer at the Hsinta power plant in the southern city of Kaohsiung, a major coal-fired station that provides around a seventh of Taiwan's power. The incident caused an ultra-high voltage substation to trip, leading to the power failure.

Hydro and other power plants are being brought on line to provide electricity, Taipower said.

Economy Minister Wang Mei-hua told reporters back-up power supply was at 24% when the incident happened, saying it was not triggered by insufficient electricity supply, the root cause of May's major power outages when Taiwan was in the midst of a drought.

She said it was not immediately clear on what triggered the problem at the Hsinta plant, but power should start being restored in southern Taiwan from midday.

"I am very sorry for this major loss of electricity, and am extremely apologetic to the inconvenience caused especially for the south," she said.

Parts of northern Taiwan, including the capital Taipei, also lost power. The presidential office said President Tsai Ing-wen has ordered the government to investigate and restore power as soon as possible.

A livestream of Tsai's meeting with the visiting former U.S. Secretary of State Mike Pompeo in Taipei has been cancelled, it added.

The Hsinchu science park, home to many large semiconductor companies such as TSMC, said it was not experiencing power outages, and the Taipei city government said the mass transit system was operating as normal.

The southern Tainan Science Park, where TSMC also has plants, said it experienced a sudden drop of voltage in the morning, but that there was no impact on production.

Taiwan's transport ministry said three trains on the high-speed rail line connecting northern and southern Taiwan were affected but normal service has now resumed.

Last year's two major power outages had triggered criticism over the government's power policy, and Tsai has vowed to scrutinise electricity management.

(Reporting by Yimou Lee and Ben Blanchard; Editing by Edwina Gibbs and Kenneth Maxwell) ((ben.blanchard@thomsonreuters.com;))