COLUMBIA, S.C. -- Scientists have been preparing for decades for next week's total solar eclipse. But people living along its path have just a few more days until their communities are inundated with millions of tourists.

It’s uncommon to see crowd control roadblocks outside a museum, but on Monday a observatory in South Carolina will be packed with thousands of people watching the total solar eclipse.

"We'll have Band-Aids, we'll have additional water, seating, we're actually bringing in misting tents and fans as well,” Merritt McNeely, marketing director said.

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The eclipse will travel almost 2,400 miles across the U.S. 12 million people live in that “totality” zone of complete darkness. However, 10 million visitors are expected to squeeze their way into the eclipse’s path. Populations in some cities could double.

A market in Idaho is already seeing more people buy bottled water and other basic supplies.

"We're hoping we get shipments every day, to keep up with the demand we're going to have. There's a lot of people coming through town,” Yvonne Smith, Ridley’s Customer Service Manager.

The eclipse is 70 miles wide, but many roads people are using to see it are narrow.

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South Carolina says its National Guard is ready to support first responders if needed. Meanwhile, Oregon’s Governor has gone one step further and already activated its National Guard to deploy additional resources.