A flash flood emergency was declared in areas north of Orlando as the region was hit by about a foot of rain, the National Weather Service said.

The declaration covered Sanford, Lake Mary and Heathrow, the service said. Nearby Central Orange, Seminole and South Central Volusia were also under flash flood warnings.

“This is a particularly dangerous situation,” the service said. “Seek higher ground now! Life threatening flash flooding of low water crossings, small creeks and streams, urban areas, highways, streets and underpasses.”

Parts of the region have seen more than 16 inches of rain within 24 hours, with more than 9 inches in the last six hours, making the storm a 1,000-year flood event in the Orlando area and to the north.

-ABC News’ Max Golembo and Kenton Gewecke

More than 2.5 million customers were without power in Florida at about 5:30 a.m. on Thursday, the state’s providers said.

Ian’s winds slowed to 65 mph early on Thursday morning, downgrading the system to a tropical storm, the National Hurricane Center said.

“The Hurricane Warnings along the east and west coasts of the Florida peninsula have been changed to Tropical Storm Warnings,” the center said.

-ABC News’ Max Golembo

Florida Governor Ron DeSantis will be holding his next press conference on the latest developments of Hurricane Ian at 8:45 a.m. ET at the State Emergency Operations Center in Tallahassee.

President Biden, meanwhile, will visit FEMA headquarters in Washington, D.C. to receive an update on Hurricane Ian at 12 p.m. ET.

While Hurricane Ian is expected to become a tropical storm on Thursday, the storm has battered southwest Florida and has left more than 2 million people without power so far.

Despite water receding in Fort Myers following Hurricane Ian's destructive path across Florida, 80% of the city is still without power, while 70% is without water, Mayor Kevin Anderson told ABC News Live Prime.

Anderson said the most important thing is to get electricity and water back up and running for residents, especially since it's still hot and humid in the area and people need air conditioning and water.

"Tomorrow, we're expecting the delivery of the pods with the water and food and ice and we'll be setting up delivery stations," he said. "Again, the problem is it's very, very difficult to live here without air conditioning."

Fort Myers has performed about 200 rescues and counting, according to the mayor.

"The crews were out and they're probably still out there working now, getting the roads cleared and getting the roads where they're traversable so that emergency vehicles can respond," Anderson said.