Power failures were reported in many parts of Taiwan on Thursday following what the presidential office said was "an incident" at a power plant.
The blackouts occurred after 9 am (0100 GMT) across the island, from the capital Taipei to central Taichung city and southern Pingtung county, reports said.
The electricity failures came as President Tsai Ing-wen was set to meet former US secretary of state Mike Pompeo.
They also came a day after a visit by a delegation of former US security officials, a trip denounced by Beijing, which sees Taiwan as its territory and denounces any official ties the island has with other countries.
The Presidential Office said an initial probe showed the blackouts were caused by "an incident" at a power plant in southern Kaohsiung city.
While power supply at the president's office was normal, it said a scheduled live stream of Tsai's meeting with Pompeo was cancelled.
"President Tsai has instructed the cabinet and relevant agencies to clarify the cause of the incident... and resume power supplies as soon as possible," the statement read.
State-run Taipower said a malfunction occurred at Kaohsiung's Hsinta power plant, the island's third-largest coal-fired station which supplies around a seventh of Taiwan's power.
It then caused an ultra-high voltage station in neighbouring Tainan to trip, which led to the blackouts, it said.
The outage hit about 5.5 million homes across Taiwan, the company said, of which 4 million have since had power restored.
Economic minister Wang Mei-hua told reporters the Hsinta plant has been cut off from the power system after the incident, with hydro and other power plants being brought online to supply electricity.
TV footage showed police officers directing cars as traffic lights failed and some shops were forced to stay closed due to the lack of power.
Taiwan High Speed Rail said an unspecified number of its trains were affected by the power outage.
Taiwan Railways Administration said some of its trains operating in southern Tainan, Pingtung and central Nantou have been delayed or suspended.
The island does occasionally experience large power outages, particularly during warmer seasons when demand spikes.
In 2017, Taiwan's economic minister resigned following an outcry over massive power failures across the island, affecting more than six million households.
Blackouts also hit in May last year as demand spiked during a heatwave.
© Agence France-Presse
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