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Outsourced call centers in India remain open despite a Monday crash to the power grid in Northern India that left as many as 370 million residents sweltering and in the dark.

The massive power outage -- the worst to hit India in a decade -- halted hundreds of trains and forced hospitals and airports to use backup generators. But business must go on -- even when the lights, however temporarily, go out.

WNS operates call service facilities for the STAR Alliance network of airlines, T-Mobile, Virgin Atlantic, and more out of Dehli, where the blackout took place. The company said that its facilities had been hit by the outage.

“Delhi Metro operations were … affected largely. The major shifts affected were the early morning shifts,” Keshav R. Murugesh, Group CEO, told FoxNews.com. After rolling over to backup gas and diesel generators, and by activating support centers elsewhere, services were kept online. “None of our businesses were affected,” a spokesman added.

Hariprasad Hegde, global head of operations for the massive outsourcing company Wipro Technologies, said it was unaffected by the outage. “Operations at Wipro’s facilities across India continued as normal. Wipro facilities have a strong backup infrastructure and contingency plans to deal with such eventualities,” he told FoxNews.com.

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Several technology firms contacted by FoxNews.com confirmed that outsourced call centers were still operational.

Some smaller businesses weren’t as lucky as those giant corporations, however, and were forced to shut for the day. Buildings were without water because the pumps weren't working. Muslim families were forced to eat their pre-dawn meals by candlelight before beginning their daytime Ramadan fast. "It was really difficult," said farmer Mohammed Zaman.

The northern grid crashed about 2:30 a.m. because it could no longer keep up with the huge demand for power in the hot summer, officials in the state of Uttar Pradesh said. However, Power Minister Sushil Kumar Shinde said he was not sure exactly what caused the collapse and had formed a committee to investigate it.

The grid feeds the nation's breadbasket in Punjab, the war-wracked region of Kashmir, the burgeoning capital of New Delhi, the Dalai Lama's Himalayan headquarters in Dharmsala and the world's most populous state, the poverty stricken Uttar Pradesh.

By late morning, 60 percent of the power had been restored in the eight northern states affected by the outage, and the rest was expected to be back on line by the afternoon, Shinde said. The grid was drawing power from the neighboring eastern and western grids as well as getting hydroelectric power from the small neighboring mountain kingdom of Bhutan.

Shinde deflected criticism, pointing out that the United States and Brazil also had huge power failures in recent years.

"I ask you to look at the power situation in other countries as well," he said.

Uttar Pradesh Power Corp. chief Avnish Awasthi blamed the grid collapse on states drawing more than their allotted power to meet the summer demand.

The Associated Press contributed to this report.