Bangladesh today launched a probe into the nationwide blackout, the worst since 2007, after a key transmission line supplying electricity from India broke down, plunging homes, businesses and even the Prime Minister's office into darkness.

"We have formed a technical committee to find out the specific reason for the power outage. We will comment after they report," state minister for power and energy Nasrul Hamid said. 

There were loud cheers in the capital, Dhaka, as lights came back in phases.

The interconnection line used for transmission of 450 megawatts at Bheramara in Kushtia district, tripped yesterday, an official at Power Development Board (PDB) said.

The high-voltage transmission line runs from Baharampur in West Bengal, India, to Bheramara in south-west Bangladesh. 

Bangladesh began importing electricity from India in October last year. 

The outage was triggered by excessive electricity supply from India, Chief Engineer Power Grid Company of Bangladesh Aksad Ali was quoted as saying by the Dhaka Tribune.

"India normally supplies 250 MW to 350 MW to the High Voltage DC substation. But, the country supplied 444 MW power to the substation on yesterday that triggered the technical glitch," Ali was quoted as saying by the paper. 

The sudden vacuum caused disruption of power generation at all plants across the country. 

Terming the blackout as "blessing in disguise", Hamid said the government had decided to establish a backup of the entire system to avert any similar incident in the future.