Filling most of the Bay of Bengal, Cyclone Phailin made landfall around 9.25pm local time, with winds recorded around the 125mph mark. The eye of the storm collapsed just before it hit land, spreading the hurricane-force winds more widely.
The storm was expected to affect 12 million people, most of them in the densely populated states of Odisha and Andhra Pradesh.
The army was last night on standby for emergency and relief operations and food packages were ready to be dropped.
Even before the cyclone made landfall, coconut trees in villages along the coast were bent and broken in the gusting wind, electricity poles were brought down and roads were littered with debris.
Two people were killed by falling trees and a third when the walls of her mud house collapsed.
Terrified children clung to their mothers as they sought shelter. Most towns along the coast were deserted but there were still some people trying to flee. Some took refuge in temples, others crammed into auto-rickshaws and headed inland to makeshift camps.
"This is one of the largest evacuations undertaken in India," said Shashidhar Reddy, vice-chairman of the National Disaster Management Authority. He estimated that more than 440,000 people had fled from their homes.
The size of the storm made extensive damage to property more likely, he said, adding: "Our priority is to minimise loss of life."
India's weather department warned of extensive damage to mud houses, major disruption of power and communication lines, and the flooding of rail tracks and roads. Flying debris is another threat.
"In a storm of this magnitude there is the potential for widespread damage to crops and livestock in the low-lying coastal areas and houses completely wiped away," said Kunal Shah, the head of the aid group World Vision's emergency response team in India. "While we are praying this storm loses intensity, we're also preparing."
London-based storm tracking and prediction group Tropical Storm Risk classed the storm as Category 5 - the strongest rating. The US navy's Joint Typhoon Warning Center in Hawaii predicted maximum sustained winds of about 138mph and gusts up to 167mph.
Many of the people along the affected coast are subsistence fishermen and farmers, who live in mud-and-brick or thatched huts.
In 1999, a typhoon battered the same region, killing 10,000 people.
India's disaster preparations have improved significantly since then and aid workers praised precautions for Cyclone Phailin such as early warnings, stocking of rations in shelters and evacuations.
"A lot has been learned since 1999 and my guess is that while there could be extensive damage to property and crops, the death toll will be much less," said G Padmanabhan, emergency analyst at the US Development Programme.