India has issued a "red alert" for a massive cyclone heading toward its east coast, forcing authorities to evacuate nearly half a million people out of the path of Cyclone Phailin.

Weather forecasters say the storm is expected to make landfall late Saturday and will be one of the largest to ever hit India.

Heavy rains are already pounding coastal villages. Families are trekking through the rain to shelters as gusts of wind snap branches from trees.

The skies were almost black at midmorning in Bhubaneshwar, the capital of Orissa state, about 100 kilometers from the coast.

Orissa's Special Relief Commissioner said people who had earlier been reluctant to move are "now willing" in the face of Phailin's 220 kilometer per hour winds, which could increase. A storm surge of well over 3 meters is expected, inundating a large part of the coastal area.

Pictures from weather satellites late Friday showed Cyclone Phailin so large that it covered virtually the entire Bay of Bengal as it headed toward the Indian states of Orissa and Andhra Pradesh.

The United Nations and European Union's Global Disaster Alert System warned Friday that 6.5 million people are likely to face torrential rains and damaging winds.

Cyclones in the Bay of Bengal are common this time of year, frequently wreaking havoc and causing mass deaths in coastal India and Bangladesh. A cyclone hit Orissa state in 1999, killing at least 10,000 people.

Some weather predictors have likened Phailin's size and intensity to Hurricane Katrina, which tore through the U.S. Gulf Coast and New Orleans in 2005, killing more than 1,000 people.