Rescuers were searching Sunday for four crew members of a cargo ship that overturned and caught fire near a port on the Georgia coast, but the efforts ran into trouble amid the flames and instability of the ship, the U.S. Coast Guard said.

The ship was carrying vehicles when it listed heavily in St. Simons Sound, about 120 kilometres south of Savannah.

The Golden Ray cargo ship ran into trouble in the early morning.

U.S. Coast Guard Capt. John Reed said of the 23 crew members and one pilot on board, 20 were safely rescued from the ship before rescuers determined the situation — as smoke and flames appeared — was too risky to go further inside the vessel. The vessel was just offshore in view of beachgoers on the shoreline.

Reed said rescue teams were trying to stabilize the 200-metre vehicle carrier to continue their search for the missing crew, but they have been unable to determine if the fire has been extinguished. The U.S. Coast Guard tweeted later in the afternoon that one of its groups, called the Atlantic Strike Team, was preparing to depart to the site to assess what it called a complex situation.

A damage assessment team from the <a href="https://twitter.com/USCG?ref_src=twsrc%5Etfw">@USCG</a> Atlantic Strike Team prepares to depart from <a href="https://twitter.com/hashtag/USCG?src=hash&ref_src=twsrc%5Etfw">#USCG</a> Station Brunswick. The team is assessing the impacts of the Golden Ray and are just one of many specialized teams working diligently in the complex response. <a href="https://t.co/gU4cPYV96Y">pic.twitter.com/gU4cPYV96Y</a> —@USCGSoutheast

"Once salvage professionals have determined the vessel to be stable... we will identify the best option to continue our rescue efforts for the four crew remembers who remain on board," Reed said at a news conference Sunday afternoon.

Search and rescue operations involve federal, state and local agencies. U.S. Coast Guard Lt. Lloyd Heflin said rescuers remained on the scene.

"They continue to do what they can. It is a complex situation. We're looking not just for the safety to be able to rescue the people that are on board, but also to be able to provide safety for our crew. It's ongoing," he said.

The Coast Guard said it was notified by a 911 call around 2 a.m. loca time of a capsized vessel in the sound. Petty Officer 3rd Class Ryan Dickinson said it isn't clear whether weather conditions caused the ship to lurch. Hurricane Dorian brushed past the Georgia coast last week on its path north.

Officials say they are unsure whether an earlier fire on board the disabled cargo vessel has been put out. (The Associated Press)

The Coast Guard said the overturned ship hasn't released any pollutants so far, but mitigation responses are ready in case they're needed.

The cause of the incident remains under investigation.

The Golden Ray is flagged out of the Marshall Islands and was headed to Baltimore, Md., according to the website 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 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.