Cyclone Phailin barrelled into the impoverished states of Andhra Pradesh and Orissa just after 9pm on Saturday (0230 AEDT Sunday) and would continue to wreak havoc along a 150-kilometre stretch of coast for six hours, the country's meteorology service said.
"Very severe cyclone Phailin has just started crossing the coast near Gopalpur" in Orissa, L.S. Rathore, the director general of the Indian Meteorological Office, told reporters.
"The reported wind speed is 200 km/h."
Rathore said Phailin would remain "a very serious cyclonic storm" for another six hours before losing its power.
"Landfall has started happening, the eye is moving at 10 to 15 km/h."
Even before the cyclone made landfall, strong winds had torn away trees and ripped through flimsy homes.
At one stage, the storm packed gusts of up to 240 km/h as it churned over the Bay of Bengal, making it the most powerful cyclone to hit the area since 1999, when more than 8000 died, the Indian weather office said.
Authorities said they expected three-metre storm surges, with torrential rain also threatening floods in low-lying areas in Orissa and Andhra Pradesh.
"I dread this. It's as if the world is coming to an end," 23-year-old student engineer Apurva Abhijeeta said from Puri, 70 kilometres from Orissa's state capital Bhubaneswar.
Heavy waves pounded the coast as terrified locals made their way to solid buildings, cramming into packed rickshaws and buses.
Relief efforts were under way, with free food being served in shelters.
"Everyone's in trouble so I've kept my shop open to help them," said shopkeeper Susil Kumar Singh, the owner of one of the few stores still operating in Bhubaneswar.
"The storm's going to get really heavy soon. Right now, there's no drinking water and trees are falling down all around."
Further south in Visakhapatnam, fishermen frantically sought to secure their boats while farmers tethered livestock in the afternoon.
Others watched the rough surf as wave after wave crashed into the shore.
Large boats could be seen anchored out at sea, while the biggest port in Orissa, in Paradip, has shut down.
Officials put the number of people evacuated from the coastal areas of Orissa and Andhra Pradesh at more than half a million.
Home Minister Sushilkumar Shinde told reporters 450,000 had been moved in Orissa and around 100,000 in Andhra Pradesh.
The army's National Disaster Response Force (NDRF) said 1200 of its troops had been sent to Orissa and a further 500 to Andhra Pradesh.Do you have any story leads, photos or videos?