Maria Prensa was packing her belongings as the Caribbean Fantasy ferry prepared to dock in Puerto Rico after a calm, overnight trip from the Dominican Republic.

Suddenly, she smelled smoke. "I asked, and they told me it was nothing, that it was under control," the 64-year-old Dominican said.

An hour later, she found herself tumbling down an emergency slide with helicopters whirring overhead, one of more than 500 passengers and crew members who had to abandon the burning ship Wednesday about a mile off Puerto Rico's north coast. U.S. Coast Guard boats carried them into San Juan's harbor with help from other agencies and even private vessels.

"It was like something out of a movie," Prensa said on shore, wiping away tears. "You're in the middle of the ocean and there's a fire. Imagine that."

The fire erupted in the engine room, and it apparently had been burning for some time before the alarm was sounded.

Gyno Funes said he and another mechanic were in the control room when a hose carrying fuel burst and caught fire.

"We were trying to extinguish it for two hours, but couldn't," the other mechanic, Marlon Doblado, told The Associated Press.

Passengers told of leaving breakfasts half-eaten and abandoning luggage when the alarm went off.

The mostly Dominican passengers included dozens of school-age athletes headed to competitions in Puerto Rico, including a cycling team, a girls' volleyball team and a boys' baseball team. Among them was Soribel Soto's son, who was dressed in his team uniform like the other athletes.

Several people panicked, Soto said.

"Some of them passed out," she recalled as she and other passengers sat barefoot near the San Juan harbor waiting for a bus to take them to the ship's original destination. Nearby, several dogs sat patiently in cages waiting to be reunited with their owners.

Dozens of people were strapped onto gurneys and taken to a triage area or nearby hospitals to be treated for heat stroke, shock and dehydration. Among them was a man hooked to an IV line who was cradling a bawling baby clad only in a diaper.

More than 100 people were treated at the scene and 24 were hospitalized. Among the latter were three women who dislocated their ankles and a man who broke his leg while going down the emergency slide.

None of the injuries were life-threatening and everyone was expected to recover, said Angel Crespo, director of Puerto Rico's Emergency Management Agency.

The Coast Guard said it had begun an investigation into what caused the fire.

Officials with American Cruise Ferries, which operates the Panamanian-flagged ship built in 1989, did not return messages for comment. The ferry travels several times weekly between Puerto Rico and the Dominican Republic.

A ProPublica investigation found that the Coast Guard had discovered 107 deficiencies during 61 inspections of the ship since 2010. The most recent checks found no major faults, but a January 2015 inspection stated that oil fuel lines should be screened or protected in some way to avoid any spray or leakage onto ignition sources.

It was unclear what would happen to the ship, which was grounded offshore.

Officials with Puerto Rico's Natural Resources Department said that as a precaution, they removed two large manatees from the area that had been recently released into the wild. They also expressed concern about dozens of nearby turtle nests that might be exposed to any oil spills.

All passengers had arrived in the San Juan harbor by afternoon.

Blas Martinez, from the Dominican Republic, said he was grateful he was already on deck when the ship's alarm went off: "They told us, 'Evacuate because there's a fire that we cannot control.'"

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Danica Coto on Twitter: www.twitter.com/danicacoto