Three regional electricity grids have collapsed in India, affecting 600 million people in one of the world's biggest-ever blackouts.
Hundreds of coalminers are reported to be trapped underground because the blackout has immobilised lifts.
Hundreds of trains have stalled and traffic lights are not working, causing widespread traffic jams.
The massive failure - a day after a similar but smaller one - has raised serious concerns about India's outdated infrastructure and the government's ability to meet its huge appetite for energy as the country aspires to become a regional economic superpower.
Power Minister Sushil Kumar Shinde blamed Tuesday's collapse on states taking more than their allotted share of electricity.
"Everyone overdraws from the grid," Shinde told reporters.
"Just this morning I held a meeting with power officials from the states and I gave directions that states that overdraw should be punished. We have given instructions that their power supply could be cut."
The new power failure affected people across more than a dozen states - more than the entire population of the European Union.
The blackout was unusual in its reach, although its impact was softened by Indians' familiarity with frequent blackouts and the widespread use of backup generators for major businesses.
Shinde said officials were working to get power restored as quickly as possible.
The outages came just a day after India's northern power grid collapsed for several hours. Indian officials managed to restore power several hours later, but in the early afternoon on Tuesday the northern grid collapsed again.
In West Bengal, express trains and local electric trains were stopped at stations across the state. Crowds of people thronged the stations, waiting for any transport to take them to their destinations.
Chief Minister Mamata Banerjee said it would take at least 10 to 12 hours to restore power and asked office workers to go home.
India's demand for electricity has soared along with its economy in recent years, but utilities have been unable to meet the growing needs.
India's Central Electricity Authority reported power deficits of more than eight per cent in recent months.
The power deficit was worsened by a weak monsoon that lowered hydroelectric generation and kept temperatures higher, further increasing electricity usage as people seek to cool off.
But any connection to the grid remains a luxury for many. One-third of India's households do not even have electricity to power a light bulb, according to last year's census.