The U.S. military is preparing to deploy field hospitals to New York and Seattle, Defense Secretary Mark Esper said on Monday, as he acknowledged for the first time that the coronavirus pandemic could impact military readiness.

The Pentagon has already announced a string of deployments to bolster the domestic response to coronavirus outbreaks, including sending hospital ships to Los Angeles and New York City. The Army Corps of Engineers is preparing to convert hotels and dormitories into treatment facilities for sick patients.

U.S. officials have noted that field hospitals, which are essentially tent facilities that can be rapidly deployed, can only handle a limited number of patients and are less suited to treating highly infectious people who need to be isolated. But they can relieve pressure on hospitals by treating patients with illnesses other than the coronavirus.

"Right now I anticipate sending a hospital to Seattle and a hospital to New York City," Esper told a news conference, adding that he had put five expeditionary units on prepare to deploy orders. "Once that's confirmed, we will look to sending to other places."

Esper said he saw the field hospitals filling a gap until the Army Corps of Engineers can get "gyms converted, hotels converted, college dorms converted" into treatment facilities.

Esper also announced more security restrictions at the Pentagon, just a day after the military reported the first death from the coronavirus at a Defense Department agency. Esper said he has not been tested for the coronavirus but was having his temperature regularly checked.

He said if U.S. troops show symptoms of infection by the coronavirus, they will be tested.

But as the number of coronavirus cases climbs and military exercises are canceled, Esper said military readiness might be impacted. Esper said 133 military personnel had been confirmed with the virus so far.

"As this virus ramps up and spreads, we'll obviously see more and more impact (on) persons in our ranks," he said. "I'm confident that while it may have some impact on readiness, it will not affect our ability to conduct our national security missions, both at home and abroad."