San Diego

Six people were rescued from the ocean off Mission Beach after an explosion aboard their boat Sunday transformed a pleasant morning whale-watching trip into a desperate scramble for survival, authorities said.

No one was seriously injured, officials said, but the boaters--including four visitors from Denmark and a San Diego woman with a heart condition--were shaken by the incident. All suffered minor burns in the explosion and subsequent fire. Three boaters were treated at Sharp Cabrillo Hospital and later released.

Two nearby craft fished the six boaters from the ocean after spotting smoke from the fire. A lifeguard rescue boat ferried the six back to shore, including the owner, Kaj Gormsen, a San Diego appliance store owner who said he had never had any problems with the boat, called Kajde, which he had owned for three years.

Officials said that the boat, a 23-foot cabin cruiser powered by an inboard gasoline engine, sank within 30 minutes of the explosion, which occurred without warning shortly before 11 a.m.

“It (the explosion) came right out of the blue air and sent us into the blue water,” said Gormsen, whose wife, Delores, has a heart condition. Gormsen is a U.S. citizen who was born in Denmark.

Along with the Gormsens, the passengers on board included Svend Larsen, Gormsen’s Danish nephew; Dora Larsen, the nephew’s wife; and Dorthe and Lene Larsen, the couple’s two daughters. The explosion tossed 11-year-old Lene Larsen into the air. The Danes have been visiting since Wednesday.

San Diego police will investigate the matter. Officials suspect an engine mishap caused the blast, but there was no definitive word on the cause.