The U.S. Centers for Disease Control and Prevention on Thursday extended indefinitely the government's March 14 no-sail order for cruise ships, noting that 100 such vessels with an estimated 80,000 crew members aboard were offshore.

The prohibition was extended to "address the health and safety of crew at sea as well as communities surrounding U.S. cruise ship points of entry," CDC Director Robert Redfield said in a statement.

The order is effective until it's rescinded, the coronavirus national emergency is over or within 100 days, the CDC said.

The centers said at least 20 cruise ships in U.S. ports and waters have crew members on board who have the virus.