The explosion occurred on Norwegian Cruise Line's SS Norway, a historic ship that has been churning the oceans for the better part of four decades. It was once in keen competition with the famed Queen Elizabeth 2 on the trans-Atlantic run.
The blast appeared to be an accident.
Police said after the explosion that two crew members died at the scene, and authorities later reported two additional deaths, including one Sunday evening at Jackson Memorial Hospital in Miami.
Fifteen crew members were brought to the hospital, and five of them are in critical condition. Victims were taken to other hospitals, but Miami-Dade officials would not say which ones.
The Norway came into the Port of Miami at the end of a weeklong Caribbean cruise around 5 a.m., with 2,135 passengers and 911 crew members on board. The fire began about two hours later, the result of an explosion likely caused by a steam leak, according to Miami-Dade Police Director Carlos Alvarez.
Alvarez says the force of the explosion tossed four crew members through an open cargo bay door into water. They were hauled back into the ship with a rope ladder.
Miami-Dade Fire Rescue workers put out the fire in about an hour.
"So far, it looks like it was just an accident," said Coast Guard Petty Officer Anastasia Burns.
Ken Hunt, 81, said he was in his cabin when he heard the explosion.
"I didn't pay any attention at first, I thought we just hit the dock. But then the lights went out," he said.
The evacuation went smoothly, though the passengers weren't told what was going on, Hunt said. Once off the ship, the passengers squeezed into a customs hall to wait.
The Norway was scheduled to sail again later Sunday, but that cruise was canceled so officials could examine the damage, Norwegian Cruise Line spokeswoman Susan Robison said. Passengers on that cruise will be given a refund and voucher for another trip.
Launched as the SS France in the early 1960s, it was the longest - if not the largest - passenger ship afloat. At 1,035 feet, it was four feet longer than the Queen Elizabeth, and 153 feet longer than the tragic Titanic. It's too long and too wide for the Panama Canal.
In 1974, thanks in large part to the oil crisis and the blossoming of the Jet Age, the oceanliner was deemed unprofitable, taken out of service, and mothballed in France. It was eventually bought by Norwegian in 1979 for $18 million - its value in scrap metal - and revamped at a cost of $120 million.
The Norway has 12 guest decks, eight lounges and bars, two swimming pools and a casino, among dozens of other amenities.
During Memorial Day weekend two years ago, Coast Guard inspectors discovered about 100 "soft patches" covering holes in fire sprinkler lines that authorities said could have failed under intense heat. The ship was held in port for a week to repair the problems.