(Updates with details from Cuba, Florida officials)
* 'Go now,' Florida gov. tells people in vulnerable areas
* Cuba at a standstill, awaiting punishing storm
* Gas hard to find in parts of Florida
* U.S. stocks open lower amid hurricane worries
HAVANA, Sept 8 (Reuters) - Hurricane Irma menaced Cuba and the Bahamas on Friday as it drove toward Florida after lashing the Caribbean with devastating winds and torrential rain, killing 19 people and leaving a swathe of catastrophic destruction.
Florida Governor Rick Scott issued a stark warning to residents to get out if they were in evacuation zones. Irma is one of the most powerful Atlantic storms in a century.
"We are running out of time. If you are in an evacuation zone, you need to go now. This is a catastrophic storm like our state has never seen," Scott told reporters, adding the storm's effects would be felt from coast to coast.
Early on Friday, Irma was about 80 miles (125 km) northeast of Cuba's northeastern coast and 450 miles (725 km) southeast of Miami. It pummeled the Turks and Caicos Islands after saturating the northern edges of the Dominican Republic and Haiti.
The "extremely dangerous" storm was downgraded from a Category 5, the top of the scale of hurricane intensity, to a Category 4 early Friday but it was still carrying winds as strong as 150 miles per hour (240 km per hour), the National Hurricane Center (NHC) said in an advisory at 8 a.m EDT (1200 GMT).
Irma hit the southeastern Bahamas on Friday, where it was forecast to bring storm surges as high as 20 feet (six meters) before brushing Cuba's central northern coast and then slamming into southern Florida on Sunday.
Cuba, where the Communist government has traditionally made rigorous preparations when the island is threatened by storms, was at a near standstill as Irma began to drive up the northern coast from east to west offshore.
Schools and most businesses were closed, hundreds of thousands of people were evacuated, and train, bus and domestic air services around the island were canceled. Airports were closing to international flights as conditions warranted.
Irma was forecast to move closer to land as it approached the center of Cuba later in the day and on Saturday, when it could seriously damage resorts on vulnerable keys. Tourists, and even the dolphins that entertain them, were evacuated. The storm was predicted to veer north, sparing western Cuba and Havana.
"DON'T BE COMPLACENT"
In several television interviews early Friday, Florida's governor pleaded with residents to leave areas designated for evacuation, although he acknowledged frustration with buying gas and handling bumper-to-bumper traffic on the roads.
"We're doing everything we can to get the fuel out," to gas stations, including police escorts, Scott told ABC's "Good Morning America" program.
Nearly one-third of all gas stations in Florida's metropolitan areas were out of gasoline, according to Gasbuddy.com, a retail fuel price tracking service.
"Don't be complacent. We're not sure exactly where this is going to go," he told CBS, adding that he expected to see 5-10 feet of storm surge.
Downtown Miami, under an evacuation order, appeared to have emptied out on Friday morning, with little traffic on the streets and public parking lots empty.
In Palm Beach, the waterfront Mar-a-Lago estate owned by U.S. President Donald Trump was ordered evacuated, media reported. Trump also owns property on the French side of St. Martin, a French-Dutch island devastated by the storm.
A mandatory evacuation on Georgia's Atlantic coast was due to begin on Saturday, Governor Nathan Deal said.
The storm was expected to "devastate" part of the United States and officials were preparing a massive response, the head of the Federal Emergency Management Agency (FEMA) said.
The storm comes two weeks after Hurricane Harvey struck Texas, claiming around 60 lives and causing property damage estimated at as much as $180 billion in Texas and Louisiana.
U.S. stocks opened lower on Friday as investors assessed the financial impact of Harvey and tracked Irma. The three major Wall Street indexes were on track to end the week lower, with many economists forecasting that third-quarter GDP will take a hit due to the hurricanes.
Democratic U.S. Senator Bill Nelson of Florida said the state was far more prepared now than when it was hit by devastating Hurricane Andrew in 1992. He also noted that local, state and federal authorities appeared to be more coordinated after learning the lessons of 2005's Hurricane Katrina in New Orleans.
"I think Florida is prepared, but when you get 155 plus mile per hour winds nobody is going to be prepared for that kind of destruction," Nelson told cable news channel MSNBC.
IRMA'S PATH OF DESTRUCTION
Irma ravaged a series of small islands in the northeast Caribbean, including Barbuda, St. Martin and the British and U.S. Virgin Islands, flattening homes and hospitals and ripping down trees.
A Reuters witness described the roof and walls of a solidly built house shaking hard as the storm rocked the island of Providenciales.
Even as they came to grips with the scale of the destruction resident of the islands hit hardest by Irma faced the threat of another major storm, Hurricane Jose. A hurricane hunter plane found that Jose had strengthened to a Category 4 storm, the NHC said on Friday. It was due to reach the northeastern Caribbean on Saturday.
The death toll from Irma has risen as emergency services got access to remote areas.
French Interior Minister Gerard Collomb said on Friday nine people were killed, at least seven were missing, and 112 others were injured after the hurricane crashed into St. Barthelemy and St. Martin.
Four people died in the U.S. Virgin islands, a government spokesman said, and a major hospital was badly damaged by the wind. A U.S. amphibious assault ship arrived in the U.S. Virgin Islands on Thursday and sent helicopters for medical evacuations from the destroyed hospital.
A man was reported missing after trying to cross a river in Haiti's Central Plateau region.
The eastern Caribbean island of Barbuda was reduced to "rubble," and one person died, Prime Minister Gaston Browne said. In the British overseas territory of Anguilla, another person was killed and the hospital and airport were damaged, emergency service officials said.
Three people were killed in Puerto Rico and around two-thirds of the population had lost electricity, Governor Ricardo Rossello said after Irma grazed the U.S. territory's northern coast. A surfer was also reported killed in Barbados.
The storm passed just to the north of the island of Hispaniola, shared by the Dominican Republic and Haiti. It damaged roofs and caused flooding and power outages as it approached the impoverished Haitian side, but spared the island a direct hit.
(Reporting by Makini Brice in Cap-Haitien, Haiti, Delana Isles in Providenciales, Turks and Caicos; Bate Felix and Dominique Vidalon in Paris; Brendan O'Brien in Milwaukee; Susan Heavey and David Shepardson in Washington; Andy Sullivan in Miami; and Colleen Jenkins in Winston-Salem, N.C.; Writing by Frances Kerry; Editing by Larry King and Jeffrey Benkoe)