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MIAMI — As the devastated Florida Keys began reopening to residents who fled Hurricane Irma, officials warned the returning islanders to bring enough supplies to sustain them for a while, because no one yet knows when water and power will be fully restored.

"The Keys are not what you left several days ago when you evacuated. Electricity, sewer and water are intermittent at best," said Monroe County Mayor George Neugent during a news conference Saturday.

Officials opened up U.S. 1 on Saturday all the way south to Marathon for residents, business owners, disaster workers and supply trucks. They also announced plans to let the same groups have access all the way to Key West starting at 7 a.m. Sunday.

Recovery efforts are well underway with the Salvation Army planning to serve 5,000 barbecue dinners Saturday night in Marathon and Key West, marking the first hot meals for many since Irma made landfall nearly a week ago.

Roads were being cleared and recovery centers are being set up in the area to help residents fill out FEMA, insurance and small business relief paperwork. Even Publix was open until 5 p.m. on Friday.

Officials had agonized over the decision to reopen the islands, knowing residents were desperate to assess the damage with their own eyes, yet worried about harsh living conditions for those who choose return.

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Curfews remained in effect and returning residents received a clear message from Keys officials — you must be self-sufficient. They encouraged residents to bring tents, small air conditioning units, food, water and medications.

Officials said their detailed hurricane plan didn't account for some unique challenges brought by Irma, which nearly wiped out parts of the middle Keys, while Key West remained in decent shape.

Two residents of Marathon Key chat while surveying the storm surge debris deposited in their neighborhood after Hurricane Irma struck the Florida Keys in Marathon, Florida, on Sept. 15, 2017. CRISTOBAL HERRERA / EPA

Getting Key West residents and businesses owners to the southernmost point remained a challenge as authorities work to keep out tourists, gawkers, looters and others who could hamper recovery efforts.

Nearly two dozen checkpoints in the hardest hit areas will be heavily staffed with law-enforcement officers to check IDs to ensure only authorized residents and relief workers get through.

Meanwhile, officials said they hope to open government offices, courts and schools in the Keys on September 28.

Further north in Broward and Miami-Dade Counties, students in two of the nation's largest school districts still don't know when they'll return to class, forcing many Florida parents to juggle childcare as they head into a second week of recovering from Hurricane Irma.

Miami-Dade and Broward counties had hoped to resume operations Monday. But dozens of schools in the two districts — which serve almost 700,000 students — are still without power. An announcement is expected this weekend. In many South Florida counties, school has not been in session since Sept. 6.

Motorists receive free gasoline from the Fuel Relief Fund group in Big Pine Key on September 16, 2017 in Marathon, Florida. Angel Valentin / Getty Images

The uncertainty put additional stress on parents trying to return to work.

For Lori Eickleberry, 45, who owns a psychology practice with two offices in South Florida, it means dragging her 10-year-old daughter to work with her.

"It's challenging but we kept busy with activities, some coloring," said Eickelberry, of Coconut Grove.

In some southwest Florida districts, classes were postponed until Sept. 25.

Irma spread a wide swath of damage across the entire Sunshine State. In southwest Florida on Saturday, officials went door-to-door Saturday warning residents who live near the Withlacoochee River north of the Tampa Bay area of the potential for record-high flooding in the coming days.

Hernando County officials said deputies, firefighters and officials with the Florida Fish and Wildlife Conservation Commission used boats to get to homes along the river to urge residents to get out as the water levels start rising, according to a news release.

The National Weather Service said a gauge at Trilby in Pasco County is at 16.3 feet (5.9 meters), with the major flood stage is at 16.5 feet (6 meters).