The U.S. Coast Guard investigated and then cleared a potential threat aboard the container ship, Maersk Memphis, at the Port of Charleston in South Carolina, authorities said Thursday.
The Maersk Memphis, which was moored at Charleston's Wando terminal, was evacuated while federal, state and local law enforcement investigated the threat, the Coast Guard said in a statement.
A one nautical mile safety zone was established around the vessel, the U.S. Coast Guard Southeast said on its Twitter account.
At around 3:45 a.m. ET, the Coast Guard said via its Twitter account that it had investigated four containers that were a potential threat and it had cleared them.
"Unified Command determines no existing threat to the port. Terminal will reopen & safety zone has been lifted," it said in a tweet.
Coast Guard Lt. J.B. Zorn told NBC that an anonymous call was received, followed within minutes by a YouTube video with similar information regarding a potential threat on board the vessel.
The Coast Guard twitter account said the original reporting source of the threat had been detained by authorities for questioning.
USCG Southeast: #Update A 1 NM safety zone has been established around the vessel while law enforcement authorities investigate the threat.
USCG Southeast: #update Unified Command determines no existing threat to the port. Terminal will reopen & safety zone has been lifted.
USCG Southeast: #update there were 4 containers where threat was posed at terminal in Charleston, SC. These have been scanned and cleared by authorities.