The Coast Guard's Seventh District said on Twitter that it was joined by local agencies with "multiple rescue assets" on the scene after the Golden Ray cargo vessel was "listing heavily" near St. Simons Sound in Brunswick, Ga.
The Coast Guard said there were 23 crew members and one pilot on board. All but four crew members have been safely evacuated from the ship, a 656-foot vehicle carrier.
"We're still conducting rescue operations. They continue to do what they can," Coard Guard Lt. Llyod Heflin said at a Sunday afternoon news conference. "It is a complex situation."
The ship was leaving Brunswick when it drastically leaned to its side early Sunday. The Coast Guard said it was notified by a 911 call at about 2 a.m. of a capsized vessel in the sound.
Capt. John Reed, commander of Coast Guard Sector Charleston, said rescuers noticed that smoke and flames began to appear as they approached the scene, and assessed the situation to be "too risky" to go inside to locate the four missing crew members.
"Once they have stabilized the vessel, [they] will try to go in to get the four who remain on board," Reed told reporters.
Reed said the fire was observed off the ship's starboard side area of the cargo and produced black smoke. In the hours since the ship tipped over, the smoke has ceased but officials have not yet determined the fire has been extinguished.
Images released by the Coast Guard showed the large ship turned to one side.
Petty Officer 3rd Class Ryan Dickinson told the Associated Press it is not known if weather conditions caused the ship to lurch. Hurricane Dorian brushed past the Georgia coast last week before being downgraded to a post-tropical cyclone. Dickinson said it was not immediately known whether there were any injuries on board.
Cmdr. Norm Witt, Commander of Coast Guard's Marine Safety Unit in Savannah, said at Sunday's afternoon news conference the incident remains under investigation, and so far the stricken ship does not appear to be a pollution hazard to area waterways. Officials, however, are putting together a pollution mitigation plan in case something changes.
Glynn County first responders told Action News JAX they helped with the response where possible, but the ultimate responsibility for handling the situation lies with the Coast Guard.
The ship, a vehicles carrier, was built in 2017 and sails under the flag of the Marshall Islands, according to the vesselfinder.com. The ship's registered owner is a South Korean company.
The Port of Brunswick is currently closed to vessel traffic, with an established emergency safety zone in St. Simons Sound. Vessels are not authorized within a half-mile of the Golden Ray, which was lying on its side.
The Port of Brunswick is a major deepwater port in Georgia, which is comprised of three terminals that makes up the facility, according to the Georgia Ports Authority.
"The port’s well-earned reputation for productivity and efficiency is heightened by its position as one of the fastest-growing auto and heavy machinery ports in North America," the GPA's website states. "Today, more than 12 major auto manufacturers, supported by three auto processors, utilize the Colonel’s Island Terminal."
The port is one of the busiest U.S. seaports for shipping automobiles. Nearly 614,000 vehicles and heavy machinery units moved across its docks in the 2019 fiscal year that ended June 30, according to the Georgia Ports Authority.
The Associated Press contributed to this report.