NEW DELHI: Half of India's 1.2 billion people were without power on Tuesday as the grids covering a dozen states  broke down, the second major blackout in as many days and an embarrassment for the government as it struggles to revive economic growth.

Stretching from Assam, near China, to the Himalayas and the deserts of Rajasthan, the power cut was the worst to hit India in more than a decade.

Trains were stranded in Kolkata and Delhi and thousands of people poured out of the sweltering capital's modern metro system when it ground to a halt at lunchtime. Office buildings switched to diesel generators and traffic jammed the roads.

"We'll have to wait for an hour or hour and a half, but till then we're trying to restore metro, railway and other essential services," Power Minister Sushilkumar Shinde told reporters.

More than a dozen states with a total population of 670 million people were without power, with the lights out even at major hospitals in Kolkata.

Shinde blamed the system collapse on some states drawing more than their share of electricity from the overstretched grid. Asia's third-largest economy suffers a peak-hour power deficit of about 10 percent, dragging on economic growth.

"This is the second day that something like this has happened. I've given instructions that whoever overdraws power will be punished."

The country's southern and western grids were supplying power to help restore services, officials said.

The problem has been made worse by weak a monsoon in agricultural states such as wheat-belt Punjab and Uttar Pradesh in the Ganges plains, which has a larger population than Brazil. With less rain to irrigate crops, more farmers resort to electric pumps to draw water from wells.

Power shortages and a creaky road and rail network have weighed heavily on the country's efforts to industrialize. Grappling with the slowest economic growth in nine years, Delhi recently scaled back a target to pump $1 trillion into infrastructure over the next five years.

Major industries have dedicated power plants or large diesel generators and are shielded from outages -- but the inconsistent supply hits investment and disrupts small businesses.

High consumption of heavily subsidized diesel by farmers and businesses has fuelled a gaping fiscal deficit that the government has vowed to tackle to restore confidence in the economy. But the poor monsoon means a subsidy cut is politically difficult.

On Tuesday, the central bank cut its economic growth outlook for the fiscal year that ends in March to 6.5 percent, from the 7.3 percent assumption made in April, putting its outlook closer to that of many private economists. -- AGENCIES