US President Donald Trump will visit Florida on Thursday to view the damage caused as Irma tore through the state.
It will be Mr Trump's third trip related to hurricanes in two weeks and he will be joined this week by his wife Melania, the first lady.
About 90,000 residents returning to the Florida Keys and Miami Beach have been warned that most fuel stations remain closed and mobile phone signals are patchy.
Some residents were allowed into the towns of Key Largo, Tavernier and Islamorada on Tuesday morning.
"Returning residents should consider that there are limited services. Most areas are still without power and water," authorities in Monroe Country said.
Irma is being linked to at least 18 deaths in the US since it struck as a category four storm on Sunday, including 12 in Florida.
Nearly 6.9 million homes were left without power in Florida, Georgia, North Carolina, South Carolina and Alabama.
Parts of the Florida Keys, the low-lying islands which bore the brunt of Hurricane Irma, have since reopened.
But entry is being restricted to residents and business owners as work continues to clear roads and check the state of bridges linking the islands