(CNN) -- Federal investigators found no stowaways aboard a ship where they reported hearing knocking coming from inside a shipping container, the Immigration and Customs Enforcement agency said Thursday.
"After a lengthy and exhaustive inspection by Department of Homeland Security officials, the search for stowaways aboard the Ville D'Aquarius has concluded with no stowaways found," agency spokesman Russ Feinstein said.
The vessel is docked at a seaport in Newark, New Jersey.
During a routine security check on Wednesday, a Coast Guard boarding team heard sounds coming from inside a container, prompting the investigation. Authorities reported that they knocked on the container and heard knocking back.
But a large contingent of federal and state officials, using X-ray machines, K-9 units, found no stowaways after searching more than 160 containers.
The Cyprus-flagged cargo ship -- which holds about 2,000 containers -- last docked in Egypt, and had made a stop in Pakistan after originating in India, officials said.
Inspectors first checked the ship around 3 a.m. Wednesday.
Just prior to docking, the inspectors tapped on the bulkhead and heard something, said Coast Guard spokesman Charles Rowe.
The Ville D' Aquarius is managed by Global Ship Lease Services Limited and is not loaded with dangerous cargo, the Coast Guard said.
The containers that were searched will be retagged, reloaded and shipped out with normal procedures, heading toward Virginia as soon as Thursday, Coast Guard spokeswoman Lt j.g. Fannie Wilks said.
"If we believe that there may be the potential of stowaways on board a cargo ship, we will search thoroughly until we can confirm that there are not," she said, adding, "This was more of a routine Coast Guard operation than most people would realize."
She could not explain the knocking, and said that four people had heard it. Searching the ship after hearing such a noise was the right thing to do, she said.
"If the same thing happened tomorrow we would do it again, to ensure safety of someone who could be a stowaway and to ensure the security of the port," she said.
CNN's Carol Cratty and Paul Caron contributed to this report.