Airlines are adding last-minute flights out of Florida after people snapped up available seats to escape Hurricane Irma.

American (AAL), United (UAL) and Delta (DAL) all said Thursday that they were adding flights leaving from South Florida in the next couple days.

Some airlines capped their fares amid reports of price-gouging. Hotel rooms in northern Florida were reportedly booking up quickly, and many gas stations ran out of fuel.

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More than 4,000 flights have already been canceled through Saturday in the Caribbean and Florida, according to FlightAware.com. The storm is expected to barrel into Florida over the weekend.

Until then, extra flights will help a few thousand more people beat the hurricane out of town.

American Airlines said it added 16 flights from Miami to Dallas, New York and Philadelphia -- a total of 3,600 seats.

The airline said it would shut down after Friday in Miami, Fort Lauderdale, Fort Myers and West Palm Beach and on Saturday afternoon in Orlando and cancel flights the rest of the weekend.

A JetBlue (JBLU) spokesman said flights leaving Florida through next Wednesday were sold out.

United was sold out through Friday and added six flights, according to a spokesman. United expected to cancel most flights to and from southern Florida from Saturday through Monday.

Delta Air Lines had seats on "very few flights" in southern Florida but more at airports farther north including central Florida, said spokesman Anthony Black.

Delta said it was adding flights and would use larger planes to add more than 2,000 seats for passengers in Irma's path in Florida, including Miami, Fort Lauderdale and Orlando -- and the Bahamas and the Dominican Republic.

Southwest Airlines (LUV) said it would cancel all flights in Fort Lauderdale, Fort Myers and West Palm Beach from Friday evening though Sunday, and suspend Orlando flights Saturday afternoon. The airline extended cancelations in Puerto Rico and the Dominican Republic through Friday and scrubbed flights in Cuba and the Bahamas Friday and Saturday.

Before selling out, JetBlue had capped fares on Florida flights at $99 to $159 each way. American capped prices at $99 in economy and $199 for premium one-way through Sept. 17, a spokesman said.

Some passengers have gone on social media this week to accuse airlines of exorbitant price hikes ahead of the storm.

Steve MacQueen, artistic director of a performing-arts center in Burlington, Vermont, said he was shocked to pay $1,725 to fly his 87-year-old mother from Fort Myers to Charlotte, North Carolina – less than a two-hour flight -- on Thursday.

"I understand when you buy at the last minute the price is always ghastly," he said in an interview. "I was expecting to pay $700, not $1,725."

A public relations consultant said a Delta ticket from Miami to Phoenix on Expedia for her friends' daughter jumped from $547 to more than $3,200.

Expedia (EXPE) spokeswoman Sarah Gavin said her company couldn't replicate the woman's story because one of the flights had sold out. She said it's likely that the first ticket was economy on both legs but that the higher price included a flight in pricier business class after economy sold out.

On any given flight, airlines sell batches of tickets with different restrictions and prices. They use algorithms to adjust prices constantly based on supply and demand. Usually the lower fares sell out first, and that happened quickly this week with flights leaving Florida, Gavin said.

Before some airlines capped fares, checks on travel search engines showed rapid price increases in flights out of Miami, with some tickets costing more than $1,000. Travel site Kayak said earlier this week that its analysis showed prices for last-minute departures from Miami, Fort Lauderdale and Orlando rose more than 25 percent from last week, when they were in the mid $300s.

Two Democrats in the U.S. Senate, Richard Blumenthal of Connecticut and Edward Markey of Massachusetts, asked for a federal investigation.

"Price gouging practices can take root during emergencies, so we further urge you to keep a close and watchful eye on airlines over the coming week to ensure airlines are not trying to make a dime off disaster," the senators said in a letter to Transportation Secretary Elaine Chao.

The airlines denied price-gouging.

George Hobica, founder of airfarewatchdog.com, said he checked several routes and did not believe prices were out of line for last-minute tickets, which almost always cost more.

"I don't think airlines would be dumb enough to consciously gouge passengers in a crisis," he said.