Taiwan faced widespread rolling blackouts Thursday after an outage at a power plant, days after the affected electricity supplier warned that drought and a heat wave were creating an energy crunch.

Officials said the cause of the outage was still under investigation and urged calm. They said power could be restored as early as the evening.

Taipower’s Hsinta Power Plant — a coal- and gas-fired facility at Kaohsiung in southern Taiwan — tripped after an equipment failure at a substation, the Taipower company said. Starting 3 p.m. local time, the supply of electricity on the island of 24 million people was restricted to 2 million households, with rolling blackouts, as repairs began.

Taiwan Semiconductor Manufacturing Co., the world’s largest contract chipmaker, said in a statement that its factories in Hsinchu and Tainan were operating normally.

While the cause of the outage was not immediately clear, power usage has soared in Taiwan amid a heat wave, while the island’s worst drought in decades has cut hydroelectricity supply by 16 percent from a year earlier, according to Taipower. The company on Tuesday had asked residents to save electricity, warning that record summer power use was expected.

On Thursday, President Tsai Ing-wen urged people to stay calm and not spread misinformation. In a Facebook post, she said rolling blackouts have begun and that the power supply would be restored.

“The detailed cause of the accident will be reported to you by the relevant government departments after a complete investigation,” she said. “Before that, please refrain from passing along unverified false messages.”

Power outages have occurred periodically in Taiwan when power plants have tripped, including in 2017 and in 1999. The Hsinta plant began operating in 1982, but Taipower said the plant’s age was not a factor.

“Power plant tripping is a protection mechanism. It works the same as the safety switch at home, so it doesn’t matter whether the power plant is old or not,” the company said.

Taiwan residents were sent a phone alert shortly before the blackouts began, but it still took some people by surprise. Kaohsiung city’s mayor, Chen Chi-mai, said in a Facebook post that some people were temporarily trapped in elevators but that no injuries were reported. He said the city’s water supply was not affected by the outage.

Alicia Chen and Lyric Li contributed to this report.