CNN  — 

The US Coast Guard was working Monday to rescue four South Korean crew members aboard a cargo ship that tipped onto its side after it began listing heavily off the Georgia coast, the South Korean Foreign Ministry said.

Rescuers are not sure where on the vessel the crew members are located, and complicating the search are the size of the ship and the fact it has watertight doors, numerous compartments and no power, Coast Guard Petty Officer 1st Class Luke Clayton said.

Video from the scene showed a red Coast Guard helicopter landing on the ship’s side mid-morning Monday.

The 656-foot Golden Ray’s crew informed authorities that the vessel was listing about 2 a.m. Sunday. By evening, it was laid over on its side in St. Simons Sound as authorities worked to stabilize the ship so they could resume rescue operations, which were stalled due to a fire on the ship, Capt. John Reed, commander of the Coast Guard Sector Charleston, said at a news conference.

Crews from the Coast Guard and other agencies responded and rescued 20 of the 24 people on board – 23 crew members and one pilot – before a fire forced them to stop, he said. The Coast Guard said the ship is carrying vehicles.

The Golden Ray lies on its side in St. Simons Sound on Sunday.

“As smoke and flames began to appear our crews, along with the Glynn County heavy rescue team, assessed that the situation was too risky to further go inside the vessel to attempt to locate the four individuals who remain missing at this time,” Reed said.

The black smoke emanating from the ship has since ceased, Reed said.

Authorities could determine that the best option is “to go ahead and right the vessel and de-smoke and de-water before we are able to actually get in there and locate the four individuals,” Reed said Sunday.

Helicopters and fire hose used in rescues

The crew members who were rescued had to escape through different parts of the ship, Coast Guard Lt. j.g. Phillip VanderWeit said. Some were hoisted into helicopters while others were lowered – in some cases by fire hose – into boats, he said.

Coast Guard footage showed an MH-65 Dolphin helicopter hovering over the Golden Ray as crew members were lifted to safety.

They were rescued around 4 and 5 a.m., VanderWeit said.

The National Transportation Safety Board is supporting the investigation, the agency said in a tweet, with two NTSB investigators assigned to the incident.

The International Seafarers’ Center in Brunswick provided food and clothing to between 18 and 20 crew members, the center’s director, Vicki West, said.

The crew members are Filipino and South Korean, she said, and were provided with bags of hygiene items, socks, games and Bibles.

The ship, sailing under the flag of the Marshall Islands, was bound for Baltimore, where it was expected to arrive Monday, according to

No signs of pollution, official says

In the meantime, “pollution mitigation efforts” are underway, according to Cmdr. Norm Witt of the Coast Guard’s Marine Safety Unit Savannah.

After the crew members are rescued and the boat is stabilized, salvage crews will find the best way to removed the ship without creating an environmental incident, the Coast Guard’s Clayton said. There is no sign any pollutants have entered the water, he said early Monday.

The cause of the incident is part of an ongoing investigation, officials said.

A longshorewoman who said she was part of the crew at Port Brunswick that loaded vehicles onto the Golden Ray told CNN the loading and unloading process went smoothly and nothing seemed out of the ordinary. They finished their work around 11 p.m. Saturday, she said.

Multiple agencies are assisting in the incident, including the Georgia Department of Natural Resources and the Glynn County Fire Department, according to the Coast Guard’s news release.

A swimming advisory was issued for beaches in St. Simons and Jekyll Island, the Georgia DNR’s Coastal Resources Division said in a statement, pending further information about potential environmental impacts.

The agency “will conduct water quality sampling to ensure the safety of shellfish harvesting beds and swimming beaches,” it said. “The Coastal Health District is issuing a precautionary swimming advisory until that testing can be done.”

CNN’s Natasha Chen, Eliott C. McLaughlin, Fredericka Whitfield, Amanda Jackson, Sarah Faidell and Hollie Silverman contributed to this report.