Hours ahead of its landfall in Odisha, US experts have described Phailin as the strongest tropical cyclone to affect India in 14 years.
The US Navy's Joint Typhoon Warning Center (JTWC) in Pearl Harbor, Hawaii, on Friday said Phailin is now expected to break the Indian Ocean intensity record set by the 1999 Cyclone in which at least 9,000 people were killed in Odisha.
In its latest bulletin, JTWC said the extremely dangerous Tropical Cyclone Phailin has maintained Category five strength for six hours, and is expected to remain a Category 5 storm until it is just a few hours from landfall on the northeast coast of India on the Bay of Bengal.
While strengthening, the storm has grown to nearly half the size of India itself.
Jeff Masters, founder of Weather Underground in Ann Arbor, Michigan, wrote in his blog that he expects that Phailin will weaken slightly before hitting the coast, due to interaction with land, and hit as a Category 4 storm with winds of 145 - 155 mph.
The 1999 Odisha Cyclone hit land with top winds of 155 mph.
There is good reason to be concerned when a major tropical cyclone forms in the Bay of Bengal, he said.
Twenty-six of the thirty-five deadliest tropical cyclones in world history have been Bay of Bengal storms, he added.
During the past two centuries, 42 per cent of Earth's tropical cyclone-associated deaths have occurred in Bangladesh, and 27 per cent have occurred in India, he wrote.
"It's going to cause pretty complete devastation on the coast where it hits," he told The Washington Post.
Andhra Pradesh has set up a round-the-clock control room in the State Secretariat in Hyderabad.
The control room numbers are: 040-23456005/23451043 and Fax- 040-23451819.
Emergency control room numbers - 08942 240557 and +91-652838191 in Srikakulam district.
Toll free number 180042500002 was announced as the Phailin emergency number.
The helpline number of the Odisha Central Control Room - 0674-2534177.