NEW DELHI — A powerful cyclone whose spinning arms engulfed much of the Bay of Bengal weakened Sunday morning as it crashed into India’s eastern coast, flooding homes and roads throughout the region and disrupting electricity and communications.

The authorities evacuated about 800,000 people, one of the largest such evacuations in India’s history. The storm’s maximum sustained winds, which were approximately 124 miles per hour when the storm made landfall about 9 p.m. Saturday, had dropped to less than half that strength nine hours later.

At least five people were killed in the coastal city of Gopalpur because of heavy rain and high winds before the storm made landfall, officials said. The storm was expected to drop up to 10 inches of rain over the next two days in some areas.

The Indian predictions before the storm hit were less alarming than those from the meteorological authorities in the United States. Late Friday, the United States Navy’s Joint Typhoon Warning Center said the storm, then barreling across the Bay of Bengal, had maximum sustained winds of 161 m.p.h., with gusts reaching 196 m.p.h. — making it similar to a Category 5 hurricane, the most severe.