Two socialites’ ferry jaunt between Florida’s ritzy Fisher Island and a Miami Beach causeway ended in horror when their Mercedes-Benz rolled overboard with them inside, dooming them to drown, authorities said.

Emma Afra, 63, and Viviane Brahms, 75, were seated in Afra’s blue Benz when the luxury car, parked at the front of ferry behind what looked like a lightweight, canvas barrier, rolled off the Fisher Island ferry and into the chop during a run at about 4 p.m. Tuesday, according to the Miami-Dade ­Police Department.

By the time rescuers were able to fight through fierce currents to reach the car at about 10:30 p.m., both Afra — who lived on the uber-exclusive island once home to Oprah Winfrey and Mel Brooks — and Brahms, a New Yorker who lived in the Westchester town of Harrison, had drowned.

The bodies of the tragic women were found in the Benz locked in an embrace, according to the ­Miami Herald.

“It’s a terrible tragedy,” said a woman who answered the door Wednesday at Brahms’ $1.8 million Harrison mansion but declined to give her name. “She was an amazing woman.”

With no apparent warning, the 2019 Benz had rolled off the deck and splashed into the 50-foot deep channel, according to the US Coast Guard.

Sources told the Herald Wednesday that they believe Afra might have forgotten to put the Mercedes in park and hit the gas pedal in a panic when the ­vehicle started rolling.

Witness Robert Berg, who was captaining a nearby fishing charter, told the Herald the deck was open at both the front and back, with little more than a lightweight barrier.

A photo of the craft obtained by ABC affiliate WPLG TV shows a deck packed with cars save for one empty spot — just feet behind the barrier that appears to have been knocked down.

Afra — who, according to ­Miami police was busted for DUI in March 2018 — was known as a fixture on the city’s social scene.

In 2012 she co-chaired a dinner and auction benefitting the city’s Kristi House nonprofit — which works to end child abuse and sex-trafficking — that raised some $500,000, according to the organization’s Web site.

She has also attended several high-profile events across the Sunshine State, including a wine and food festival, and the opening of an Italian high-fashion exhibit.

Brahms in the 1990s reportedly was an owner of the Red Zone nightclub on West 54th Street in Manhattan, then a hot spot among the city’s club kids.

In 2017, Afra and Brahms were pictured together attending a cocktail reception at the Upper East Side art gallery of Robert Mnuchin, the father of President Trump’s Treasury secretary, Steve Mnuchin.

Roberto Sosa, the president and CEO of the Fisher Island Community Association, confirmed the deaths in a statement.

“It is with heavy hearts that we share the news of the tragic loss of life of Emma Afra and Vivian Brahms, who perished on Tuesday, Feb. 18, when the car they were riding on the ferry ended up in the water for reasons still to be determined,” he said.

The public-relations firm for Fisher Island — a community that has been consistently rated as one of the wealthiest ZIP codes in America — did not ­respond to inquiries about the precautions in place for keeping cars safe on the ferries.