The head of the US emergency agency has warned that Hurricane Irma will have a "truly devastating" impact when it makes landfall on the coastal areas of Southeastern United States.
Federal Emergency Management Agency (FEMA) chief Brock Long said Thursday that people in Florida and other southern states must observe evacuation orders as one of the strongest storms in US history surges towards the US after causing death and destruction in the Caribbean islands.
The FEMA chief said Irma would be only the fourth Category Five hurricane to hit the United States since 1851 and the first since Hurricane Andrew in 1992.
"Bottom line is the majority of people along the coast have never experienced a major hurricane like this. It will be truly devastating," he told CNN. "The entire southeastern United States better wake up and pay attention," he added.
Long, whose agency is still preoccupied with the aftermath of Hurricane Harvey, which caused catastrophic flooding in parts of Texas and Louisiana last month, said around 3,000 federal emergency workers have been mobilized to deal with Irma.
Mandatory evacuation orders have so far only been issued in parts of Florida, but similar orders are expected for South Carolina, North Carolina and Georgia within the next 48 hours.
The mayor of Miami Beach in Florida has warned that Irma could have an impact of "nuclear" proportions as he urged everyone to get out of its path as soon as possible.
"I strongly urge them to please leave Miami Beach. You have friends, you have family -- go visit them," Philip Levine told a local CBS-affiliated television station in Miami on Wednesday.
"This is a nuclear hurricane. They should leave the beach, they must leave the beach," he added.
The economic cost from Harvey for southeastern Texas has been estimated from $70 to $200 billion, ranking it among the costliest storms in US history.