Investigators in Philadelphia continue to search the cargo ship where they found more than 17 tons of cocaine Tuesday in what's being called one of the biggest drug busts in U.S. history. Officials told CBS News there could be 30 tons more on board.

What they've found so far amounts to more than 34,000 pounds of cocaine with a street value of over a billion dollars. Officials say seven containers on the cargo ship were carrying the drugs.

The ship's second mate and a crew member have been arrested and charged, admitting they helped load the cocaine onto the ship from more than dozen other boats while at sea.

The MSC Gayane had traveled from Chile to Peru, heading from Panama and the Bahamas before docking in Philadelphia. It was on its way to the Netherlands next.

The ship is owned by the Mediterranean Shipping Company, which said in a statement, "unfortunately, shipping companies are from time to time affected by trafficking problems. MSC has a longstanding history of cooperating with law enforcement."

Law enforcement is expected to give more information Thursday, after a search of containers on the ship is complete.