Millions of people huddled in shelters or in battened-down homes in Florida waiting for updates as Hurricane Irma - one of the most powerful storms ever recorded in the Atlantic - began its assault on Florida with winds nearing 215 kilometers an hour, drenching rain and catastrophically high seas.
The National Hurricane Center forecast potentially deadly storm surges - water driven ashore by the winds - of up to 4.6 meters.
As the northern edge of the storm reached the Florida Keys archipelago off the tip of southern Florida, lashing rains and winds knocked out power to hundreds of thousands of people on the mainland.
"Pray for us," Florida Governor Rick Scott said in a television interview as his state braced for the massive storm, which has already left a trail of death and destruction through the Caribbean.
Irma, which prompted one of the largest evacuations in US history, is a Category 4 hurricane. A day after hitting Cuba's northern Coast, it was on a path that would take it along Florida's Gulf of Mexico coast near population centers including Tampa and St Petersburg.
Forecasters also warned tornadoes could form in large portions of the state.
Officials in Florida have ordered a total of 6.3 million people, or about a third of the state's population, to evacuate, creating massive traffic jams on highways and overcrowding shelters.
One woman in Miami's Little Haiti neighborhood delivered her own baby, with medical personnel coaching her on the phone because emergency responders were not able to reach her.
Irma, which killed at least 22 people in the Caribbean, was likely to cause billions of dollars in damage to the third-most-populous US state.
Irma comes just days after Hurricane Harvey dumped record-setting rain in Texas, causing unprecedented flooding, killing at least 60 people and leaving an estimated US$180 billion (HK$1.4 trillion) in property damage in its wake. Almost three months remain in the Atlantic hurricane season, which runs through November.
Meanwhile, Florida authorities warned that shooting bullets into the storm won't help keep you safe.
The sheriff's office was responding to a Facebook event page created two Florida men inviting people to shoot at Irma. The page reads: "Yo so this goofy Let's show Irma that we shoot first. The invitation presumably was a joke, but 80,000 people indicated they were "going" or "interested" in the event.
REUTERS, ASSOCIATED PRESS