St Petersburg - Residents huddled in shelters watching for updates as Hurricane Irma began its assault on Florida early on Sunday as a Category 4 storm, lashing the area with winds near 215km/h and drenching rain.Irma's northern eyewall reached the lower Florida Keys and the US National Hurricane Center said the hurricane was expected to remain a powerful storm as it moved through the Florida Keys and near the state's west coast.As of 08:00 EDT on Sunday, the hurricane was centered about 30 km east-southeast of Key West, Florida, and was moving north-northwest at 13km/h. The Key West International Airport measured sustained winds of 80km/h with a gust of up to 113km/h, according to the hurricane centre.The National Weather Service issued tornado warnings for a wide swath of Monroe, Miami-Dade and Broward counties in South Florida. The band of rain and tornado producing cells was moving quickly, officials said. There were no immediate reports of tornadoes touching down.READ: Hurricane records broken in 2017In the Tampa Bay area, access to all of Pinellas County's barrier islands, including the popular spring break destination of Clearwater Beach, was shut off.The leading edge of the immense storm bent palm trees and spit rain across South Florida, knocking out power to hundreds of thousands of homes and businesses, as the eye approached Key West.As the hurricane's eye approached the Florida Keys early on Sunday, 60-year-old Carol Walterson Stroud and her family were huddled in a third floor apartment at a senior center in Key West."We are good so far," she said in a text message just before 05:30 "It's blowing hard."Stroud was with her husband, Tim Stroud, and granddaughter, Sierra Costello. Their dog Rocky was also riding out the storm.Stroud said she planned to step outside once the eye of the hurricane passed over. She said she has stood in the eye of a hurricane before and it's "total peace and quiet".During the eyeHowever, Key West Police urged anyone riding out the storm in that city to "resist the urge" to go outside during the eye. "Dangerous winds will follow quickly," police said in a Facebook post.Florida Governor Rick Scott had warned residents in the state's evacuation zones on Saturday: "This is your last chance to make a good decision." About 6.4 million people were told to flee.But because the storm is 560km to 450km wide, the entire Florida peninsula was exposed. Forecasters said the greater Miami area of six million people could still get life-threatening hurricane winds and storm surge of 1m to 2m.Irma was at one time the most powerful hurricane ever recorded in the open Atlantic with a peak wind speed of 300km/h last week. It left more than 20 people dead across the Caribbean and as it moved north over the Gulf of Mexico's bathtub-warm water of nearly 90 degrees, it was expected to regain strength.Meteorologists predicted Irma would plow into the Tampa Bay area on Monday morning. The area has not been struck by a major hurricane since 1921, when its population was about 10 000, National Hurricane Center spokesperson Dennis Feltgen said. Now around three million people live there.The latest course also still threatens Naples' mansion- and yacht-lined canals, Sun City Center's retirement homes, and Sanibel Island's shell-filled beaches.Irma's course change caught many off guard and triggered a major round of last-minute evacuations in the Tampa area. Many businesses had yet to protect windows with plywood or hurricane shutters. Some locals grumbled about the forecast, even though Florida's west coast had long been included in the zone of probability."For five days, we were told it was going to be on the east coast, and then 24 hours before it hits, we're now told it's coming up the west coast," said Jeff Beerbohm, a 52-year-old entrepreneur in St Petersburg. "As usual, the weatherman, I don't know why they're paid."Storm surgeNearly the entire Florida coastline remained under hurricane watches and warnings, and the latest projections could shift again, aiming the worst of the storm at other parts of the state.Forecasters warned of storm surge as high as 4.5m."This is going to sneak up on people," said Jamie Rhome, head of the hurricane center's storm surge unit.The westward shift prompted Pinellas County, home to St Petersburg, to order 260 000 people to leave, while Georgia scaled back evacuation orders for some coastal residents. Motorists heading inland from the Tampa area were allowed to drive on the shoulders.At Germain Arena not far from Fort Myers, on Florida's southwestern corner, thousands waited in a snaking line for hours to gain a spot in the hockey venue-turned-shelter."We'll never get in," Jamilla Bartley lamented in the parking lot.The governor activated all 7 000 members of the Florida National Guard, and 30 000 guardsmen from elsewhere were on standby.In the Orlando area, Walt Disney World, Universal Studios and Sea World all were closing on Saturday. The Miami, Fort Lauderdale, Tampa and Orlando airports shut down.Given its mammoth size and strength and its course up the peninsula, it could prove one of the most devastating hurricanes ever to hit Florida, and inflict damage on a scale not seen here in 25 years.Hurricane Andrew smashed into suburban Miami in 1992 with winds topping 265km/h, damaging or blowing apart over 125 000 homes. The damage in Florida totalled $26bn, and at least 40 people died.