Stranded rail passengers wait on a platform in the hope train services will resume following a power outage (AP)
Factories and workshops across India are up and running again, a day after a major system collapse led to a second day of power outages and the worst blackout in history.
About 620 million people were left without electricity after India's northern, eastern and north-eastern grids failed on Tuesday afternoon.
It was the second massive outage in as many days, coming just after the country had recovered from Monday's failure of the northern grid, which left 370 million people powerless.
Electricity workers struggled throughout the day on Tuesday to return power to the 20 affected states, restoring most of the system in the hours after the crash. Power minister Veerappa Moily told reporters that by Wednesday morning power had been fully restored across the country.
Mr Moily, who took over the top power position on Tuesday, said an investigation into the crisis had been launched and he did not want to point fingers or speculate about the cause.
Other officials said the blackout might have been the result of states drawing too much power from the grid. Some analysts dismissed that explanation, saying that if overdrawing power from the grid caused this kind of collapse, it would happen all the time.
The Confederation of Indian Industry said the two outages cost business hundreds of millions of pounds, though they did not affect the financial centre of Mumbai and the global outsourcing powerhouses of Bangalore and Hyderabad in the south.
The group demanded the widespread reform of India's power sector, which has been unable to keep up with soaring demand for electricity as the economy has expanded and Indians grow more affluent and energy hungry.
The power minister cautioned there would be no quick solution to the power crisis, saying the government is looking at immediate and longer term measures to address power scarcity. Part of the problem is that India relies on coal for more than half its power generation and the coal supply is controlled by a near state monopoly that is widely considered a shambles.
A recent survey showed nearly all the coal-fuelled plants had less than seven days of coal stock, a critical level, and many power plants were running below capacity, according to Samiran Chakraborty, head of research at Standard Chartered, a financial services company.