Federal health officials are prepared to help with emergency medical needs of people affected by Hurricane Irma and are putting particular emphasis on patients who already are relying on ongoing medical care to live.

State and federal health officials have told Floridians to leave their homes in order to avoid what is expected to be a devastating impact from Hurricane Irma. Florida's Department of Health has evacuated 11 hospitals and 142 other hospital facilities, and federal officials have assembled disaster medical assistant teams.

And while government agencies are focused on helping people access food, water, transportation and shelter, over the long-term they face a major challenge to monitor patients with chronic conditions who will struggle to access the care they had before the storm devastated their homes and neighborhoods.

"The biggest challenge from a health standpoint in these storms is making certain that those people with chronic illnesses and chronic diseases are able to hook back up with their providers," Health and Human Services Secretary Tom Price said during a news conference Friday. "When you get displaced from your pharmacy and from your doctor or clinic for a period of time, then those chronic health challenges become more acute."

HHS has identified people who depend on electricity for their care, including people on dialysis or who need oxygen, and sent their information to the state, whose officials will individually contact patients. Price said more than 5,000 patients on dialysis had been identified as well as 20,000 other people who rely on electricity and 6,700 people who rely on oxygen for their care.

He encouraged people to leave their homes to be safe from the storm and has declared a public health emergency in Florida, which allows medical resources to get to people faster and can temporarily lift government regulations. For instance, the federal government lifted certain prescription requirements so that people could get more of their medications for a longer period of time or refill prescriptions early.

"This remains a remarkably dangerous storm, and the window to get yourself in the right spot for weathering the storm ... is closing rapidly," Price said.

The Florida Keys, parts of Miami and Fort Lauderdale are under mandatory evacuation orders, as are coastal areas of the state. Forecasters said that the storm is expected to hit South Florida on Saturday night and proceed up the peninsula Sunday.

"I can guarantee you that I don't know anyone in Florida that is about to experience what's about to hit South Florida," said Brock Long, FEMA administrator, at a news conference on Friday. "[Residents] need to get out and listen and heed the warnings."

Earlier this week, Hurricane Irma hit the U.S. Virgin Islands, Puerto Rico, and other islands in the region as a Category 5 storm, and killed at least 10 people.

While preparing for Hurricane Irma, federal health agencies are still assisting with the fallout from Hurricane Harvey in Louisiana and Southwest Texas, where Price also had declared a public health emergency as the hurricane hit. He traveled to Texas with Trump last week.

"In terms of Harvey, we remain in the response and recovery issues that continue," Price said. "The life-saving activities are transferring to life-sustaining activities."

Federal and state officials moved patients elsewhere after healthcare facilities closed, including a peak of 30 hospitals and 26 nursing homes in Texas. The number of closed hospitals is now down to four, and officials are monitoring which pharmacies are open and how many electrical outages remain.

The Department of Health and Human Services is running temporary health centers where Price said they are treating patients for rashes or illnesses like diarrhea, nausea and vomiting. Price said in an interview with Time magazine that officials also begin vaccinating against the flu when people enter shelters. Another federal agency, the Centers for Disease Control and Prevention, is preparing to educate residents about mosquitoes as the flooding subsides, and officials are gearing up for the possibility of waterborne infectious diseases.

"Any time you have standing water for a period of time there are resulting challenges that occur," Price said, noting that officials are testing the water for contaminants or bacteria.

On Thursday, the Centers for Medicare and Medicaid Services set up a temporary waiver for people who are insured through Medicare to be able to more quickly get back medical equipment including prosthetics, crutches, walkers and hospitals beds that were lost as a result of the storm. The waiver allows patients to bypass a face-to-face meeting with a doctor as well as lengthy documentation to be able to get the medical supplies and equipment they need.

The Centers for Medicare and Medicaid Services also designated certain dialysis facilities in Louisiana and Texas as "Special Purpose Dialysis Facilities" so people who have been displaced from their neighborhoods could still get treatment. People who have renal failure need dialysis twice a week to remove excess waste and water from the blood. CMS estimates that within the areas hit roughly 20,000 people need dialysis, and Price said 13 other centers were still closed as of Friday.

"Access to care for people living with renal diseases and disorders is critical to timely treatments and monitoring," said CMS administrator Seema Verma in a statement. "This vulnerable population of people with Medicare and/or Medicaid benefits and their families are encouraged to take advantage of available resources to ensure their care is managed as we all work together to use innovative approaches to keep facilities, healthcare providers and ancillary resources available."