Florida Gov. Ron DeSantis warned Wednesday morning that Ian could potentially make landfall as a Category 5 hurricane.

“This is a powerful storm that should be treated like you would treat a tornado approaching your home,” he said. “This one has just strengthened and strengthened, and it is the real deal. So, it is going to do a lot of damage, so people should be prepared for that.”

More than 200 shelters are open in South Florida, he said.

Twenty-six states, including New York and New Jersey, have sent support to Florida, he said.

-ABC News’ Mariama Jalloh

Hurricane Ian approached Category 5 status at about 6:30 a.m. ET, with its winds topping out at 155 mph.

Only four hurricanes have ever made landfall in the continental U.S. with winds over 155 mph: Labor Day in 1935 with 185 mph winds; Camille in 1969 with 175 mph winds; Andrew in 1992 with 165 mph; and Michael in 2018 with 160 mph.

Severe Category 5 hurricanes have winds above 157 mph.

“Rapidly intensifying Ian forecast to cause catastrophic storm surge, winds, and flooding in the Florida peninsula,” the National Hurricane Center said at 7 a.m. ET.

-ABC News’ Max Golembo and Samantha Wnek

A whopping 16 feet of storm surge is possible around Fort Myers.

Up to 11 feet of storm surge is forecast for Naples while a maximum of 10 feet is expected for the Sarasota area.

"Our biggest concern as we wait for this storm to make landfall is storm surge," FEMA Administrator Deanne Criswell warned Tuesday. "In 2018, when Hurricane Michael impacted the Florida Panhandle, there were five recorded fatalities as a result of storm surge."

Click here to learn how storm surge works.

Hurricane Ian strengthened to a Category 4 hurricane on Wednesday morning, as its winds climbed to 140 mph, the National Hurricane Center said.

The storm is the first Category 4 hurricane in the Gulf of Mexico since Hurricane Rita in September 2005.

-ABC News’ Max Golembo

Lee County has received more than double the number of 911 calls it typically receives amid Hurricane Ian, according to Sheriff Carmine Marceno, as first responders have suspended their emergency response during the major storm.

"We hear your calls and are aware that Hurricane Ian was a powerful and devastating weather event," Marceno said in a social media post Wednesday evening. "We want to get to you. We want to save you. As soon as safely possible, our assets are ready to deploy to come to your aide."

Ben Abes, Lee County's public safety director, said current conditions, including flooding, make it "impossible" for first responders to go out. He said the county is tracking 911 calls and prioritizing them once first responders are able to act after the hurricane passes.

"We are aware of a number of calls of people who are stranded due to high water," he said during a press briefing Wednesday evening. "This is a scary situation. We urge you not to panic."

Lee County, which is home to hard-hit Fort Myers, Sanibel and Bonita Beach, issued a countywide curfew Wednesday evening due to the storm that is in effect until further notice.