Mosques which use loudspeakers to call for prayers five times a day fell eerily silent and houses were darkened.
Authorities blamed the outage in the densely-populated nation of 155 million on a transmission line failure.
Water supplies were hit as most of the pumps which lift groundwater could not function.
“I don’t know how such a disaster can happen,” fumed laundry operator Ataul Hakim.
Fish traders were furious at a lack of ice to keep their supplies fresh. One trader, Robiul Islam, said he would lose 5,000 taka ($700) as he could not preserve his stock.
The blackout occurred just before midday.
Power was restored in some parts of the capital Dhaka after several hours, but engineers were working late into the night to restore the supply nationwide.
“We hope we can restore most of the power by midnight. We regret the failure and we urge people to be patient,” power ministry spokesman Saiful Hasan told AFP.
Local media said the problem stemmed from a technical problem at an electrical substation distributing power from India, but government officials would not confirm the reports.
All areas linked to the national electricity grid had been hit, another senior power ministry official, Masud Alberuni, told AFP.
The national grid “tripped” and “all the power-generating stations in the country automatically shut down in a cascading effect,” Alberuni said.
The outage marked the first time the whole country has been without power since November 2007 when Bangladesh was hit by a devastating cyclone, Alberuni added.
The blackout hit at the weekend, lessening the impact on industry. Temperatures have also passed their summer peak, limiting complaints over the stoppage of fans and air conditioning units.
Many people in rural parts of chronically energy-short Bangladesh, accustomed to regular power cuts lasting many hours, did not know that the blackout was nationwide.
The presidential palace, the prime minister’s office, government offices and television stations were all hit by the outage.
“There’s no signs of hope. The place looks like a ghost town,” said Aminur Rahman, who lives a short distance from the prime minister’s office in Dhaka.
“We’ve come out of the house as it’s so strangely dark inside.”
Hospital intensive care units functioned on back-up generators, but ward patients suffered.
Power returned to Dhaka’s international airport after several hours during which it ran on generators, officials said.
The blackout occurred after a transmission line transporting power from India through a “high-voltage” substation failed, Chowdhury Alamgir Hossain, a director of state-run Power Grid Company of Bangladesh, told the Dhaka Tribune newspaper.
But government officials declined to identify the transmission line.
Dhaka began importing power from India late last year through a line stretching from India’s eastern state of West Bengal to southwestern Bangladesh.
“We are investigating the reason for the power cut. A probe committee will be formed,” said state power minister Nasrul Hamid.
Hours after the outage began, authorities were only able to supply around 500 megawatts of power — far short of normal daily demand of around 7,000 megawatts, officials said.
Electricity supplies in Bangladesh, one of the world’s poorest countries, are vastly overstretched.
As in many other parts of the developing world, the rise in energy consumption has outdistanced economic growth, with an expanding middle-class and increasing industrialisation imposing heavier loads on scant generating capacity.
The outage evoked memories of a blackout in India two years ago that was one of the world’s worst in recent times. Some two-thirds of India’s states suffered outages when three of the nation’s five power grids failed at once.
The Indian outage sparked serious doubts about the ability of the country’s rickety electricity infrastructure to meet the nation’s aspirations to transform into an economic superpower. -AFP