Coast Guard Capt. Peter Gautier told New Orleans broadcaster WWLTV that 28 people were on board a rig in the shallow waters in the Gulf of Mexico at the time of the incident. Two people were killed, two more were missing and four others were taken from the rig by air transport to an area medical center.
The Coast Guard official said the rig wasn't producing oil at the time of the incident. Fluid from a pipe under service by maintenance workers may have caused the explosion, he said.
Kirk Trascher, a spokesman for rig owner Black Elk Energy, told Houston broadcaster KHOU that no oil was released into the gulf.
Last month, the independent company announced plans to start drilling and carry out "major rig work" in the first of 23 wells in the Gulf of Mexico during the month of November. The company explained the November startup was part of a multiyear program in the region.
The incident occurred one day after the U.S. Justice Department fined British energy company BP $4 billion for the 2010 oil spill in the Gulf of Mexico. That accident left 11 rig workers dead and lead to the worst accidental offshore oil spill in the history of the industry.
BP was charged with manslaughter for each of the rig workers killed in the 2010 accident.
The Coast Guard said it was investigating the latest incident.