Bangladesh has restored power in most of the country, a day after a transmission line bringing electricity from neighbouring India failed, causing a nationwide blackout, officials have said.

The blackout, which affected more than 150 million people, was the country's worst since a 2007 cyclone knocked out the national grid for several hours, and again exposed inefficient and dated infrastructure that has held back development in the South Asian nation.

Power was restored in Dhaka, the capital, and in other major cities too, but it was not clear how many people were still without electricity, which had been cut across Bangladesh at around noon on Saturday after a "technical glitch" that led to a cascade of failures throughout the national power grid, with power plants and substations shutting down.

Al Jazeera's Tanvir Chowdhury, reporting from Dhaka, said that 80 percent of the country's power has been restored, with 20 percent left to go.

"Calm has returned to the country, but most of the industries and the emergency service hospital clinics were badly hit [by the blackout]," he said.

Our correspondent also said that the government could not provide either timeframe for when total power supply would be restored or an exact reason as to why all the electricity shut down.

"The government formed an investigative committee to find an answer," he said.

Dhaka's hospitals and the international airport continued to operate after the blackout on Saturday with emergency generators. But many offices had to send their employees home.

Tawfiq-e-Elahi Chowdhury, energy adviser to Prime Minister Sheikh Hasina, said late on Saturday that he expected the supply would be back to normal by Sunday afternoon.

'Loss in confidence'

"This is terrible," said Mohammad Hasan, a resident of Dhaka's upscale Bashundhara neighbourhood. "We had some confidence in the government over last few years that the power sector was improving slowly. But what is this?"

Bangladesh is considered one of the most energy-poor nations, with one of the lowest per capita electricity consumption rates in the world. The country is often able to produce only some of its 11,500-megawatt generation capacity.

Power outages blamed on old grid infrastructure and poor management are common in Bangladesh.

Bangladesh has tried to improve its energy situation, extending access to electricity to about 3.45 million more people since 2008.

Last year, it started to import electricity from India through the 400-kilovolt transmission line, which runs from Baharampur in the Indian state of West Bengal to the town of Bheramara in southwestern Bangladesh.

It also has signed agreements with energy companies in Russia, Japan, China, and the United States to build power plants and improve energy infrastructure.

Source: Al Jazeera and agencies