Hurricane Irma's eyewall slammed into the lower Florida Keys on Sunday, lashing the island chain with fearsome wind gusts.
The eye of the Category 4 storm was 24 kilometers southeast of Key West, bringing winds up to 210 kilometres per hour and threatening dangerous storm surges.
Around 1,20,000 Indian-Americans reside across Florida while thousands of them live in the now-dangerous zones of Miami, Fort Lauderdale and Tampa.
Miami and Tampa appeared 'ghost towns' as nervous residents, many of whom struggled to cope with abandoning their homes, moved to safer places following mandatory evacuation notices.
The National Weather Service said Irma regained strength as a Category 4 storm -- after being downgraded to Category 3 for more than 12 hours -- as it moved to Florida.
Earlier, a 127 kmph gust was recorded as Irma drew closer to Florida, CNN reported.
The Indian embassy in the United States has opened a round-the-clock helpline number and rushed senior diplomats to Atlanta to lead relief efforts for Indian-Americans stuck in the region.
The hotline number is 202-258-8819. Embassy officials said India's Ambassador to the US Navtej Sarna was closely monitoring the situation.
Sandeep Chakravorty, India's consul-general in New York, was in Atlanta overseeing preparation for relief efforts from a 24X7 control room.
The Indian Consulate in Atlanta tweeted helpline numbers (+14044052567 & +1678179393) for people seeking assistance.
'Atlanta is fully prepared to take care of evacuees from Florida. Some have already reached. Consulate is on call 24x7,' it said in another tweet.
External Affairs Ministry spokesperson Raveesh Kumar tweeted 24X7 helpline at High Commission of India, Kingston (+1876 833 4500; +1876 564 1378). He also tweeted email ids for Indians to contact in case of emergency: email@example.com; firstname.lastname@example.org.
The Indian Friends of Atlanta - in association with the Consulate-General of India, the Gujarat Samaj Atlanta and the Hindu Temple of Atlanta - have operationalised three shelters.
They were preparing to open more shelters and provide food. Several Indian businesses have started contributing to relief efforts.
The hurricane has almost ruined the Caribbean islands as a Category 5 storm. At least 24 people died as the storm swirled over the region and hit Cuba on Saturday on its way to Florida.
The Indian embassy in Venezuela tweeted the helpline number in Aruba, a tiny Dutch Caribbean island off the coast of Venezuela, for the situation in Sint Maarten: 00297-593-2552.
The helpline numbers in Curacao, a Dutch Caribbean island, is 005999-513-2407; 005999-690-2686.
The Indian embassy in the Netherlands said countrymen affected by Irma can reach them on: 0031643743800.
Those affected in Cuba, Dominican Republic and Haiti can contact Indian authorities on emergency no. +5352131818 or email them at: email@example.com.
Almost entire Florida was under hurricane warning. At least 36 million people have been affected by the hurricane.
President Donald Trump reviewed preparedness with his cabinet colleagues at Camp David in Maryland. He asked federal and state agencies expedite assistance to affected areas.
"This is a storm of enormous destructive power, and I ask everyone in the storm's path to pay heed to all instructions from government officials," Trump said.
Florida Governor Rick Scott asked people to move out of the danger zones as soon as possible. "The state has never seen anything like this. The storm's surge can kill you."
The US Army has so far deployed more than 7,400 soldiers and US Army Corps of Engineers civilians on the US Virgin Islands, Puerto Rico, and the continental US.
The Pentagon said the army has over 140 aircraft, 650 trucks, 150 boats prepared, additional resources on standby.
AccuWeather, a forecast weather agency, warned Irma will unleash destructive winds, flooding, rain and inundating seas.
"Unfortunately, there is no way the US is going to avoid another catastrophic weather event," AccuWeather president Joel N Myers said.
"[It will be] the worst single hurricane to hit Florida since Hurricane Andrew in 1992," Myers said.