Hurricane Irma is currently tearing through the Caribbean and is on track to reach Florida and the USA.
Hurricane winds are expected to reach the southern tip of Florida before 8am AST on Saturday.
Electric company officials in Florida have planned for the worst and are likely to shut the nuclear plants in Turkey Point and St Lucie.
Spokesman for Florida Power and Light (FPL), Peter Robbins, said the decision of whether to shut down the reactor will be made “well in advance” of the Category five storm making landfall.
Mr Robbins said: “If we anticipate there will be direct impacts on either facility, we’ll shut down the units.
“Based on the current track, we would expect severe weather in Florida starting Saturday, meaning we would potentially shut down before that point.”
FPL has defended the safety of its nuclear plants, which are located along the Atlantic coast and are exposed to very strong winds and storm surges.
St Lucie’s nuclear plant survived Hurricanes Frances and Jeanne in 2005 and Wilma in 2006.
Mr Robbins said: “For the top of the plant to be underwater, if there were flooding on the plant, we could absolutely stay safe.
“We designed the plant to handle that, the systems at the plant to handle that.”
FPL is the third-largest electric utility in the United States and serves around 10 million people across almost half of Florida.
President of FPL, Eric Silagy said: “Should Irma’s worst fears be realised, our crews will likely have to completely rebuilt parts of our electric systems.
“Restoring power through repairs is measured in days; rebuilding the electric system could be measured in weeks.”
It comes as the eye of the hurricane passed north of Puerto Rico early Thursday, battering the US territory with high winds and heavy rains and leaving nearly 70 per cent of the population without electricity, Governor Ricardo Rossello said.
The National Hurricane Center (NHC) said the eye of Irma was moving west-northwest off the northern coast of the Dominican Republic on Thursday morning.
Irma’s precise course remained uncertain but it was likely to be downgraded to a Category 4 storm by the time it makes landfall in Florida, according to the NHC.
Irma has become a little less organised over the past few hours but the threat of a direct hurricane impact in Florida over the weekend and early next week was increasing, the NHC said.
Prime Minster Theresa May has deployed a British military taskforce to the Caribbean and has re-deployed Royal Navy warship HMS Ocean to the region.