Miami ? An explosion and fire in the boiler room of a docked cruise ship killed at least four crew members Sunday and injured more than 15 others, authorities said. The blast did not cause any injuries among the more than 2,100 passengers.

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, a spokeswoman said.

Fifteen crew members were brought to the hospital, and five of them were in critical condition. Victims were taken to other hospitals.

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, port director Charles Towsley said. The fire began about two hours later, the result of an explosion likely caused by a steam leak, Miami-Dade Police Director Carlos Alvarez said.

The force of the explosion tossed four crew members through an open cargo bay door into water, Alvarez said. They were hauled back into the ship with a rope ladder.

Miami-Dade Fire Rescue workers put out the fire in about an hour, Coast Guard Petty Officer Anastasia Burns said.

“So far, it looks like it was just an accident,” Burns said.

Steam rises from the vents of the Norwegian Cruise Line's SS Norway about a half hour after an explosion and fire in the boiler room occurred at the Port of Miami, Miami, Fla. Sunday's explosion killed at least four crew members and injured more than 15 others before the flames were extinguished, authorities said. None of the ship's more than 2,100 passengers was injured.

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 4 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.