The workers were evacuated Tuesday from the jack-up Hercules 265 rig, which was off the coast of Louisiana working for Walter Oil & Gas Corporation.

The Bureau of Safety and Environmental Enforcement said the blow-out occurred during completion work on the sidetrack well to prepare it for production.

The well is flowing gas and no oil is being released.

BSEE inspectors conducting a fly-over reported a light sheen of gas covering 0.5 miles by 50 feet.

They said it was dissipating almost immediately, but affirmed they would be keeping a close eye on Walter's efforts to clean up the area and stop the flow of gas.

According to the Wall Street Journal, Walter officials initially said that it appeared some of the shear arms on the rig's blow-out preventer failed to close and seal off the well.

However, it has since said that it was not sure what caused the reported blowout and was investigating.

A firefighting vessel is expected to be on location today, with water and foam firefighting abilities.

Walter Oil will be conducting a site assessment prior to beginning any work on the well. BSEE will be reviewing and approving all plans and procedures to stop the flow of gas and secure the well.

While it was a gas well, the incident has brought back memories of the Deepwater Horizon incident, when the failure to seal off a blow-out preventer led to the largest offshore oil spill in US history.