A human error at a key power plant knocked out power across Taiwan's 17 cities and counties yesterday, triggering the resignation of a minister.

Shopping and business districts in Taipei were left in darkness for hours last night until power was fully restored at 9.40pm.

Economic Affairs Minister Lee Chih-kung told Premier Lin Chuan that he will tender his formal resignation by as early as today, said a Cabinet spokesman.

President Tsai Ing-wen, whose approval rating recently hit a record low of 29.8 per cent, apologised on her Facebook page last night. She wrote: "Electricity is not just a problem about people's livelihoods but also a national security issue. A comprehensive review must be carried out to find out how the electric power system can be so easily paralysed by human error."

The power trip, which happened at 4.52pm and lasted two minutes, caused blackouts across Taiwan, including some smaller industrial areas. But the power outages did not affect high-speed rail and metro train services.

To restore normal power supply, the government rationed electricity for three hours across the island from 6pm yesterday. People were reportedly stuck in lifts or caught in Taipei traffic jams caused by non-working traffic lights.

At a news briefing before he resigned, Mr Lee apologised for the inconvenience caused and vowed to get to the bottom of the matter, adding that the authorities will not "dodge any responsibility".

Government-run utility firm Taipower said the electricity rationing affected over 6.7 million households, or half of Taiwan's 13 million households and commercial units.

This is one of the worst power outages in Taiwan in nearly two decades. A huge earthquake in 1999 caused massive power outages for about three weeks.

Mr Derek Chen, chairman of government-controlled oil company CPC Corporation, said a human error at Taoyuan city's Tatan Power Plant, Taiwan's biggest natural gas power plant, caused six generators to stop working. This affected the supply of four million kilowatts of electricity.

He said investigations are ongoing to see how the error was made and if there was any negligence.

Taiwan has been at risk of a power shortage after a recent typhoon knocked down a power transmission tower in Hualien city in eastern Taiwan. The government has imposed power rationing such as switching off air-conditioning in offices, despite an ongoing heatwave.