(Adds comment from director of Defense Health Agency)

By Idrees Ali and Phil Stewart

WASHINGTON, March 19 (Reuters) - Tens of thousands of U.S. National Guard troops could be activated to help U.S. states deal with the fast-spreading coronavirus outbreak, the head of the U.S. National Guard said on Thursday.

The National Guard, part of the reserve component of the U.S. Armed Forces, has already been called up in 27 states, including New York, to assist with cleaning public spaces and to deliver food to homes.

General Joseph Lengyel, chief of the National Guard Bureau, said that a total of about 2,000 troops have been activated so far and he expected that number to double by the weekend.

"It's hard to tell what the exact requirement will be, but I'm expecting tens of thousands to be used inside the states as this grows," Lengyel said during a Pentagon press briefing.

The National Guard could, for example, assist local law enforcement efforts under state control, he said. But that is something it cannot do if it is federalized, Lengyel said, adding he was not aware of any such plans and did not think it was a good idea. "That would not make sense in this situation," Lengyel said.

A Pentagon spokeswoman said the Defense Department was not considering federalization of the National Guard.

Nearly 9,000 cases of the novel coronavirus have been reported in the United States, with more than 3,000 in New York state, according to state health departments.

"It's a historic event, unlike any we have faced in recent years," Lengyel said.

Dealing with the coronavirus outbreak is an unusual mission for the National Guard, best known for assisting during national disasters like hurricanes and supplementing the U.S. military overseas or during times of war. More than 21,000 National Guard members are currently abroad.

Lengyel compared the coronavirus outbreak to a national disaster of unprecedented scale.

"It's like we have 54 separate hurricanes in every state and territory and the District of Columbia... Unlike a hurricane, we don't know when this is going to dissipate or move out to sea," he added.

Even within the military, the disease is taking a toll. The Pentagon said that 51 U.S. military service members had been diagnosed but, as of Thursday, none were hospitalized and two had recovered.

In a sign of the impact the outbreak was having, the director of the Defense Health Agency said on Thursday that calls to the U.S. military health system's nurse advice line had surged by about 500% in just the past few days. (Reporting by Idrees Ali and Phil Stewart Editing by Bernadette Baum and Diane Craft)

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