A propeller-driven seaplane carrying 20 people crashed just off Miami Beach within sight of the city's high-rises Monday, killing at least 19 of those aboard, authorities said. Witnesses said the plane exploded in flames as it came down, and the FBI joined the investigation.

Amateur video obtained by a cable news network showed the main part of the aircraft slamming into the water followed by a flaming object trailing thick black smoke.

Scuba divers and rescuers in speedboats struggled to reach the victims, but as evening fell, they found no sign that anyone survived.

The Chalk's Ocean Airways plane — a twin-engine Grumman G-73T Turbine Mallard — went down around 2:30 p.m. after taking off from Miami for the island of Bimini in the Bahamas, the Federal Aviation Administration said. It hit the water within sight of the beach.

The Coast Guard said 19 bodies were found. The 1940s-era plane was carrying two crew members and 18 passengers, including three infants, authorities said.

Because of the witness reports of an explosion, the FBI sent agents to assist in the investigation, but there was no immediate indication of terrorism or sabotage, said Judy Orihuela, spokeswoman for the FBI's Miami field office.

"It's too soon to say whether we are going to get involved," Orihuela said. "We're just going to check it out."

Chalk's is a small air carrier that is not required to conduct federal security screening of passengers and their luggage, said Dale Karlen, federal security director at Fort Lauderdale-Hollywood International Airport.

With many schools already closed in advance of the holidays and Christmas week traditionally one of the biggest times of the year for tourism, the beach was relatively busy, and dozens of beachgoers saw the plane go down. Dozens more gathered to watch the rescue.

As Coast Guard helicopters hovered over the crash site, some surfers remained in the water, only a few hundred feet away. Some surfers used their boards to rush toward the spot where the plane went down.

Sandy Rodriguez, 14, said he saw the plane flying low with white smoke trailing from it and flames coming from the bottom. The right wing then fell off as the plane went down, he said.

"It exploded in the air and one of the wings flew out of there. The other part of the plane was on fire, and it just went straight down," said Maurice D'Giovianni, 42, a surfer who was in the water at the time.

Coast Guard spokesman Dana Warr also saw the crash from an island in a channel known as Government Cut that cruise ships and freighters take past South Beach into the Port of Miami.

"Everything looked normal, I saw the aircraft take off like it does every other time. I didn't think anything of it when I saw the black smoke from the pier, until I then heard the Coast Guard alarms go off," he said.

Coast Guard Capt. James Maes said the main part of the fuselage was submerged in about 35 feet of water that is subject to strong tidal currents because of the narrow ship channel. Divers continued to search after dark for the final victim.

Ship traffic in and out of the port will be suspended indefinitely, Maes added, including three large cruise ships that had been scheduled to depart Monday afternoon.

The National Transportation Safety Board also sent a team to investigate.

The skies were cloudy, but there was no rain or lightning at the time of the crash.

Garred Gadaon, 34, said his sister-in-law and her 13-year-old daughter were on the plane.

"We had a tragic death today with many of our family members and our friends. It doesn't seem real. Chalk's has always been a safe plane for us," he said while standing outside the Miami Beach Police Department.

Bahamas Minister of Tourism Obie Wilchombe, who is also a member of parliament for Bimini, said on local television that 11 people aboard the plane were from Bimini, about 50 miles east of Miami.

Bahamian Prime Minister Perry G. Christie said the country's consul general in Miami had already met some family members at the scene of the accident.

"The nation wishes to express its deepest condolences to the people of Bimini on their apparent loss," Christie said in a statement.

Coast Guardsmen and emergency workers wearing protective suits hauled bodies up from rescue boats, rushing to find victims before darkness fell. Law enforcement speedboats, divers and helicopters took part in the search and were joined by others in private boats, on personal watercraft and on surfboards.

The aircraft that went down was built in 1947 and is registered to Seaplane Adventures LLC in Greenwich, Conn., according to FAA records.

The plane had a clean safety record with no reported incidents for more than 21 years. In February 1984, the elevator trim tab, which controls pitch, failed and caused the steering column to shake. In April of that year, the landing gear failed to retract, and investigators found the nose gear assembly was overstressed.

No passengers or crew were injured in either incident, according to the records.

Chalk's Ocean Airways flies between Miami and the Bahamas, using planes that take off and land on the water. Chalk's aircraft have been featured in TV shows such as "Miami Vice." Its seaplanes take off in view of the port and the multimillion-dollar homes that dot islands in the bay.

Founded by Arthur "Pappy" Chalk in 1919, the airline thrived during Prohibition, taking bootleggers, their customers and customs agents to Bimini. According to the airline, its most famous regular passenger was Ernest Hemingway, who flew to Bimini to go big-game fishing.

One of its planes was hijacked to Cuba in 1974 and the company has since had a policy of not carrying enough fuel to get to Havana.

Two years later, the airline was sold to Resorts International, which owned properties on Paradise Island. Donald Trump bought it in 1988 and sold it a few months later to Merv Griffin.

The owner as of 1995 was Seth Atwood of United Capital Corporation of Illinois/Atwood Enterprises. Chalk's was bought by Florida businessman Jim Confalone in 1999 and renamed Chalk's Ocean Airways.

According to its Web site, the carrier flies 17-passenger Turbine Mallards, which can operate from land or water.

Chalk's was in the midst of an "extensive refurbishment" of its airline fleet, according to the company's web site.

The company's Grumman G-73 aircraft — like the one that crashed — had engines converted from older piston-driven models to turboprops, as well as upgrades in avionics and improvements to the plane's interior, the company said.

Chalk's general manager Roger Nair said Monday's crash was the airline's first accident with a passenger fatality. The National Transportation Safety Board database indicates no fatal accidents involving passengers for Chalk's since 1982, when the database began.

Chalk's only crash involving fatalities happened in 1994, when two pilots died in a crash of their seaplane near Key West.