NEW DELHI - Factories and workshops across India were up and running again Wednesday, a day after a major system collapse led to a second day of power outages and the worst blackout in history.

An estimated 620 million people were left without electricity after India's northern, eastern and northeastern grids cascaded into failure 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 had left 370 million people powerless.

Electricity workers struggled throughout the day Tuesday to return power to the 20 affected states, restoring most of the system in the hours after the crash. India's new Power Minister Veerappa Moily told reporters that by Wednesday morning power had been fully restored across the country.

Moily, who took over the top power position Tuesday, said an investigation into the crisis has 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 dollars, though they did not affect the financial centre of Mumbai and the global outsourcing powerhouses of Bangalore and Hyderabad in the south.

Like many, the group demanded the widespread reform of India's power sector, which has been unable to keep up with the soaring demand for electricity as the economy has expanded and Indians grow more affluent and energy hungry.

The power minister cautioned that there would be no quick solution to the power crisis, saying the government was 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-fueled plants had less than seven days of coal stock, a critical level, and many of the country's power plants were running below capacity, according to Samiran Chakraborty, head of research at Standard Chartered, a financial services company. Government bureaucracy has made it difficult to bring more plants online.

In addition, vast amounts of power bleeds out of India's antiquated distribution system or is pirated through unauthorized wiring. Farmers, with a guarantee of free electricity that is driving many state electric boards to bankruptcy, have no incentive to conserve energy.

The power deficit was worsened this year by a weak monsoon that lowered hydroelectric generation, spurred farmers to use pumps to irrigate their fields long after the rains would normally have come, and kept temperatures higher, keeping air conditioners and fans running longer.

The government faced criticism for promoting Sushil Kumar Shinde from power minister to home minister in the middle of the day Tuesday, even as the outages continued. The promotion had been planned as part of a Cabinet reshuffle by Prime Minister Manmohan Singh.

The Times of India newspaper said moving Shinde "is like changing the captain of the Titanic when it's reeling after hitting a giant iceberg."

Shinde, whatever his blame for the outage might be, at least would have more experience to deal with the fallout than a brand new minister, the paper said in a front-page editorial.

Earlier on HuffPost:

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  • A traffic jam following power outage and rains at the Delhi-Gurgaon road on the outskirts of New Delhi, India, Tuesday, July 31, 2012. (AP Photo)

  • An Indian barber holding a candle, has a haircut for a customer at his shop in Kolkata, India, Tuesday, July 31, 2012. (AP Photo/Bikas Das)

  • A building is seen dark following a power outage in Kolkata, India, Tuesday, July 31, 2012. (AP Photo/Bikas Das)

  • A young Indian girl looks out from a stalled train window as passengers are stranded following a power outage in New Delhi, India, Tuesday, July 31, 2012. (AP Photo/Rajesh Kumar Singh)

  • An Indian man watches as he and others wait inside a stalled train for its services to resume following a power outage in New Delhi, India, Tuesday, July 31, 2012. (AP Photo/Rajesh Kumar Singh)

  • Indian stranded passengers wait for train services to resume at a railway station following a power outage in New Delhi, India, Tuesday, July 31, 2012. (AP Photo/Rajesh Kumar Singh)

  • Indian stranded passengers wait for the train services to resume at a railway station following a power outage in New Delhi, India, Tuesday, July 31, 2012. (AP Photo/Rajesh Kumar Singh)

  • Stranded passengers walk on railways tracks near parked trains following a power outage at a railway station in New Delhi, India, Tuesday, July 31, 2012. (AP Photo/Rajesh Kumar Singh)

  • Indian stranded passengers wait on a platform and some of them on rail tracks for the train services to resume following a power outage at Sealdah station in Kolkata, India, Tuesday, July 31, 2012. (AP Photo/Bikas Das)

  • A stranded Indian train passenger rests inside a railway coach as he waits for the train service to resume following a power outage in Kolkata, India, Tuesday, July 31, 2012. (AP Photo/Bikas Das)

  • An Indian shopkeeper fixes an electric generator at his shop in New Delhi, India, Tuesday, July 31, 2012. (AP Photo/Tsering Topgyal)

  • Pigeons sit on electricity wires along a Metro line after Delhi Metro rail services were disrupted following a power outage in New Delhi, India, Tuesday, July 31, 2012. (AP Photo/Mustafa Quraishi)

  • A handwritten notice about power failure is pasted outside a Metro station after Delhi Metro rail services were disrupted following power outage in New Delhi, India, Tuesday, July 31, 2012. (AP Photo/ Manish Swarup)

  • Commuters wait in line at a Metro station after Delhi Metro rail services were disrupted following power outage in New Delhi, India, Tuesday, July 31, 2012. (AP Photo/ Manish Swarup)