Taiwan is gradually restoring power supply, the state-run power operator said on Thursday, after 5 million households in much of the island's south were hit by an outage caused by a malfunction at a major power generation plant.

Hydro and other power plants are being brought online to provide electricity, said Taipower, which blamed a problem with a transformer at the Hsinta power plant in the southern city of Kaohsiung for a trip at an ultra-high voltage substation.

The major coal-fired station provides about a seventh of Taiwan's power.