As the grids collapsed around 1 PM, miners in Eastern Coalfields got trapped in Sodepur and Satgram in Burdwan districts of West Bengal, according to officials who said rescue efforts are on.
In Delhi, Metro commuters were trapped inside the tunnels for sometime as trains came to a halt as electricity supplies got snapped.
The Centre blamed overdrawal by states in the Eastern region for today's grid collapse. Power Grid Corp promised normalcy would be restored by 7 PM.
The states affected included Delhi, Uttar Pradesh, Haryana, West Bengal, Punjab, Jammu & Kashmir, Odisha, Bihar, Rajasthan and Assam and Union Territory of Chandigarh, covering more than half of the population.
In Kolkata, Metro Rail services were unaffected, according to state Chief Minister Mamata Banerjee. The state government declared holiday in its offices after 3 PM.
The Railways network across major parts of the country was among the worst hit services, as trains, other than those running on diesel engine, stopped midway.
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Assam witnessed large-scale power cuts throughout the state. In Orissa also, train services were hit.
The Northern Grid, which collapsed yesterday and was restored after 15 hours, again tripped today. The Eastern and North-Eastern transmission lines too failed this afternoon, worsening the power situation in the country when it is facing drought-like situation in most parts.
"Some sections are creating problems by overdrawing power," Power Grid CMD R N Nayak said.
This is probably the first time that three grids have collapsed simultaneously, MORE