Those involved in relief efforts in the Keys expect to find casualties, but Monroe County Commissioner Heather Carruthers said she expected a low count because "so many people evacuated".
Jacksonville, the largest city geographically in the country, is grappling with a record storm surge and vast flooding.
The National Hurricane Centre said the storm "should continue to lose strength and fall below hurricane intensity" during the day, as it continues its path northwards.
National Hurricane Center in Miami update at 5 a.m. on Monday.
Florida's governor is issuing urgent warnings to a third of his state's residents to evacuate ahead of a massive hurricane on track to be the state's most catastrophic ever.
"What we think we'll see on the west coast is a wholesale rebuild of our electric grid", Robert Gould, Florida Power & Light's vice president and chief communications officer, told ABC News.
Australia starts voting on same-sex marriages
People participate in a march for marriage equality of same-sex couples in Sydney, Australia, September 10, 2017. The country's Opposition Leader, Bill Shorten, said it was the law that had to change, not the gay community.
The projected path of Hurricane Irma has shifted west to Southwest Florida and may hit Tampa, which is more vulnerable to storm surge than any other USA metropolitan area. However, South Carolina will see more rain and a higher effect for severe weather Monday and this pattern will continue north towards the North Carolina coast into Tuesday. Interstate 95 in Duval County and parts of Interstate 75 and Interstate 95 in Miami-Dade County remained closed because of flooding or debris. 12,500 flights to or from Florida were canceled due to the storm.
Most of the damage includes flooding, structural, nonfunctioning stoplights, downed trees and power lines.
Utility officials said they have almost 20,000 workers helping with the restoration effort.
Georgia Gov. Nathan Deal has already declared a state of emergency for all 159 counties as Irma barrels toward the state.
Shelters are allowing people to leave but will stay open for people.
Katia made landfall in eastern Mexico late yesterday - just as the country was grappling with its worst natural disaster in a century - as a Category 1 hurricane.
Last month, Hurricane Harvey devastated much of coastal Texas and killed more than 70 people.
- Authorities report 1st death in Georgia from Irma
- James Woods on Amber Tamblyn's pick-up attempt story: It's 'a lie'
- Edith Windsor, LGBTQ Icon and American Hero, Dies at 88
- Najib, Trump meet to discuss terror fight
- North Korea slams 'vicious' US-led United Nations sanctions
- Crystal Palace name Hodgson as manager
- Family of three die after falling into volcano crater near Naples
- Destiny 2 to Remove Item With White Supremacist Logo
- Teen partygoer found dead in hotel's walk-in freezer
- Apple Watch Series 3 GPS Edition India Price and Availability Details