Authorities have launched an investigation into what caused all power plants to trip, plunging the capital, Dhaka, and other big cities into darkness.
At least 130 million people in Bangladesh have been left without power after a grid failure caused widespread blackouts, the government's power utility company said.
It remained unclear what caused Tuesday's unscheduled blackout, which hit more than 80 percent of the country shortly after 2:00 pm (0800 GMT), according to the Power Development Board.
Apart from some locations in Bangladesh's northwest, "the rest of the country is without power", spokesperson Shamim Ahsan told AFP news agency.
The normally brightly lit streets of central Dhaka and other cities were dark on Tuesday evening.
Ahsan said 130 million people or more were without electricity and it remained unclear what had caused the fault.
"It is still under investigation," he said, adding that a technical malfunction was the probable cause.
Another official said later that only 60 percent of the poor country, which is home to factories supplying garments for Western brands, had been affected.
Since then half of those affected had had their power restored by the evening, A.B.M Badruddoza, spokesperson of the state-run power grid company, told AFP.
Junior technology minister Zunaid Palak said on Facebook that power would be restored by 8:00 pm in the capital Dhaka, a megacity home to more than 22 million people.
Prices of energy as well as food and other staples have soared worldwide in the wake of Russia's attack on Ukraine in February, including in Asia.
This has wrought havoc on Bangladesh's electricity grid in recent months, with utilities struggling to source enough diesel and gas to meet demand.
The government imposed lengthy power cuts to conserve existing stocks in July, with outages lasting up to 13 hours a day at their peak.
The blackouts sparked widespread public anger and helped mobilise large demonstrations on the streets of Dhaka.
At least three protesters were killed by security forces during the rallies, partly motivated by rising cost-of-living pressures.
Around 100 others were injured during a police crackdown on one demonstration, according to the opposition Bangladesh Nationalist Party.
Bangladesh last witnessed a major unscheduled blackout in November 2014, when around 70 percent of the country went without power for nearly 10 hours.
READ MORE: EU seeks $140B to cope with energy crisis