Acting Navy Secretary Thomas Modly said Captain Brett Crozier was wrong to distribute to a wide range of people copies of an emotional, four-page letter describing the threat of the outbreak to the ship's nearly 5,000 sailors, allowing it to be leaked earlier this week to US media before top defense officials saw it.

Modly said that while there have been 114 cases of the coronavirus in the crew so far, none has been severe and Crozier overstated the severity when he suggested sailors were going to die without fast action.

Crozier "demonstrated extremely poor judgment in the middle of a crisis" in his handling of the letter, Modly said.

"It misrepresented the facts of what was going on the ship" and created "a little bit of panic" that was unnecessary, he said.

"I have no doubt in my mind that Captain Crozier did what he thought was in the best interests of the safety and well-being of his crew," said Modly.

"Unfortunately, it did the opposite."

In addition to frightening families of the sailors, he said, "it raised concerns about the operational capabilities and operational security of that ship that could have emboldened our adversaries to seek advantage."

The Roosevelt, one of two US Navy carriers in the western Pacific, is now docked in Guam where most of the crew is being offloaded and placed in shore housing to decontaminate the vessel.

The Navy said Rear Admiral Carlos Sardiello, a former captain of the Roosevelt, will replace Crozier.

By sidelining the Roosevelt, the virus outbreak has hobbled a key asset of US military readiness, though US defense officials say there are no immediate strategic threats and that the ship can be put to sea quickly if required.

Earlier this week Defense Secretary Mark Esper said adversaries' armed forces are also challenged by COVID-19.