A cargo ship flipped on its side off the coast of Georgia early Sunday morning, the Coast Guard said.

Four crew members were still missing after initial rescue efforts and were thought to still be aboard the ship.

Fox News cited Capt. John Reed, the commander of Coast Guard Sector Charleston, as saying a fire was impeding attempts to reach the four.

It is unclear what caused the ship to overturn, the Coast Guard said.

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A cargo ship flipped on its side in the Saint Simons Sound near Brunswick, Georgia, early Sunday, the US Coast Guard said. The ship, Golden Ray, could be seen smoking in photos shared by the Coast Guard.

A coalition of eight Coast Guard units including two helicopter crews rescued 20 of the 24 people on board, the Coast Guard said. Four crew members were still missing, however, and were believed to still be aboard the disabled ship.

Fox News cited Capt. John Reed, the commander of Coast Guard Sector Charleston, as saying a fire had halted rescuers' attempts to reach the four. "Once they have stabilized the vessel," he reportedly said at a press conference, rescuers would "try to go in to get the four who remain on board."

The International Seafarers' Center in Brunswick said it provided socks and hygiene items to the crew members, who are South Korean and Filipino, according to CNN.

The Coast Guard said it first learned of the Golden Ray's troubles when it was contacted by the 911 Dispatch in Georgia's Glynn County at about 2 a.m. The rescue operation was still underway at 11:07 a.m., the Coast Guard tweeted.

Golden Ray carries vehicles for a company based in South Korea, Fox News reported.

The ship flies the flag of the Marshall Islands and had previously passed waypoints in Jacksonville, Florida, and in Capetown, South Africa before overturning off the coast of Georgia, according to VesselTracker.com.

It is unclear what caused the incident, the Coast Guard said.

The National Transportation Safety Board said it was assigning two investigators to assist in determining the cause.