A rescue mission is underway for four crew members who remain unaccounted for after a cargo ship began "listing heavily" off the coast of Georgia Sunday morning, according to a news release from the US Coast Guard.

Glynn County 911 dispatch notified the Coast Guard of a capsized vessel -- the 656-foot Golden Ray, which is transporting vehicles -- in St. Simons Sound around 2 a.m., the release said.

By late Sunday morning, 20 people had been rescued from the ship, which had a crew of 24, the Coast Guard said.

Images showed a trail of smoke emanating from the ship, which the Coast Guard said was "laid over on its side."

There was a fire on board, the Coast Guard's release said. The cause of the incident is still under investigation.

Multiple agencies are assisting in the incident, including the Georgia Department of Natural Resources and the Glynn County Fire Department.