GRAND ISLE - It's been two days since search and rescue crews last heard from the missing crewmembers of a capsized lift boat in the Gulf of Mexico, officials said Thursday. 

The Coast Guard said it had searched over 6,000 square miles in the Gulf, a search radius about the size of Hawaii, as of Thursday afternoon. Six of the 19 crewmembers have been rescued, and one person is dead. 

Divers joined the search effort Thursday amid reports that the remaining crew members were likely still on board the capsized boat. 

Two crew members of the capsized lift-boat upside down off the Louisiana coast were alive and speaking with the Coast Guard for a few hours after the accident Tuesday. The new details on the search and rescue effort were released by Coast Guard sources to WWL-TV in New Orleans Thursday.

WWL and WBRZ have a news partnership.

Two crew members last radioed with the Coast Guard around 9:53 Tuesday night. They have not been heard from again. The two crew members said they were retreating from the upside-down hull of the ship, back into the interior of the vessel.

Radios were dropped by a Coast Guard helicopter above, Lt. John Edwards told WWL.

A thermal imaging device showed at least five people on the ship's hull at the time before the two crew members went back into the boat. Of the five, two retreated into the boat; two jumped off and were rescued by Coast Guard boats. One crew member fell into the water and has not been found.

In all, six crew members were rescued in the aftermath of the capsizing Tuesday. Twelve crew are still missing, including the two who were last known to be alive late Tuesday evening. It's unclear what their condition is as of Thursday.

Rescue divers attempted to tap on the hull of the vessel Thursday, hoping to find signs of life. It's unclear what was found, WWL reported.

The U.S. Coast Guard said Thursday afternoon the incident was designated a "major marine casualty" after spending more than 70 hours searching the area surrounding the overturned vessel.