Forest rangers are on high alert amid fears that the eclipse could encourage wildfires to spread across the US.

Tourists are flocking to western states like Oregon, Idaho and Wyoming, ready for the sky to go dark as the moon moves in front of the sun. But they will bring unprecedented challenges with them: with blocked roads and strained resources adding to already significant worries.

The region is already carpeted by dry wood that experts worry could light anyway. But the extra worries added by unattended campfires, discarded cigarettes, hot tailpipes and all the other danger that new campers bring.

Lunar eclipse delight for sky watchers around the world Show all 26 1 /26 Lunar eclipse delight for sky watchers around the world Lunar eclipse delight for sky watchers around the world A lunar eclipse is visible in Scottish Borders, the result of the Moon starting to move into the Earth's shadow. PA Lunar eclipse delight for sky watchers around the world A total eclipsed moon is seen from Silver Spring, Maryland, on December 21, 2010. GETTY IMAGES Lunar eclipse delight for sky watchers around the world A total eclipsed moon is pictured as seen from Silver Spring, Maryland, on December 21, 2010. GETTY IMAGES Lunar eclipse delight for sky watchers around the world A picture taken in New York shows the moon in the early stages of a lunar eclipse on December 21, 2010. GETTY IMAGES Lunar eclipse delight for sky watchers around the world A lunar eclipse is visible in Scottish Borders, the result of the Moon starting to move into the Earth's shadow PA Lunar eclipse delight for sky watchers around the world The moon is pictured during a circle of a total eclipse as seen from Silver Spring, Maryland, on December 21, 2010. This eclipse takes place just hours before the December solstice, which marks the beginning of northern winter and southern summer. Getty Images Lunar eclipse delight for sky watchers around the world The moon is pictured during a circle of a total eclipse as seen from Silver Spring, Maryland, on December 21, 2010. This eclipse takes place just hours before the December solstice, which marks the beginning of northern winter and southern summer. Getty Images Lunar eclipse delight for sky watchers around the world The moon is pictured during a circle of a total eclipse as seen from Silver Spring, Maryland, on December 21, 2010. This eclipse takes place just hours before the December solstice, which marks the beginning of northern winter and southern summer. Getty Images Lunar eclipse delight for sky watchers around the world The moon during a cycleof a total eclipse ais seen from Silver Spring, Maryland, on December 21, 2010. This eclipse takes place just hours before the December solstice, which marks the beginning of northern winter and southern summer. Getty Images Lunar eclipse delight for sky watchers around the world A total eclipsed moon is pictured as seen from Silver Spring, Maryland, on December 21, 2010. This eclipse takes place just hours before the December solstice, which marks the beginning of northern winter and southern summer. Getty Images Lunar eclipse delight for sky watchers around the world A picture taken in New York shows the moon as a total eclipse nears its peak on December, 21, 2010. During the eclipse, the Earth will align between the full moon and the sun, covering the lunar surface in shadow. The eclipse is also falling on the same day as the winter solstice in the Northern Hemisphere a rare occurrence that hasn't happened in 372 years. Getty Images Lunar eclipse delight for sky watchers around the world A picture taken in Manassas, Virginia shows the moon as the total eclipse reaches its peak on December, 21, 2010. During the eclipse, the Earth will align between the full moon and the sun, covering the lunar surface in shadow. The eclipse is also falling on the same day as the winter solstice in the Northern Hemisphere a rare occurrence that hasn't happened in 372 years. Getty Images Lunar eclipse delight for sky watchers around the world A total eclipsed moon is seen from Silver Spring, Maryland, on December 21, 2010. This eclipse takes place just hours before the December solstice, which marks the beginning of northern winter and southern summer. Getty Images Lunar eclipse delight for sky watchers around the world The moon is pictured during its circle of a total eclipse as seen from Silver Spring, Maryland, on December 21, 2010. This eclipse takes place just hours before the December solstice, which marks the beginning of northern winter and southern summer. Getty Images Lunar eclipse delight for sky watchers around the world A picture taken in Manassas, Virginia shows the moon as the total eclipse reaches its peak on December, 21, 2010. During the eclipse, the Earth will align between the full moon and the sun, covering the lunar surface in shadow. The eclipse is also falling on the same day as the winter solstice in the Northern Hemisphere a rare occurrence that hasn't happened in 372 years. Getty Images Lunar eclipse delight for sky watchers around the world In this handout photo provided by NASA, A total lunar eclipse is seen as the full moon is shadowed by the Earth on the arrival of the winter solstice, on December 21, 2010 in Arlington, Virginia. It is the first lunar eclipse that has coincided with the Winter Solstice, the shortest day of the year, since 1638. Getty Images/ NASA Lunar eclipse delight for sky watchers around the world Getty Images Lunar eclipse delight for sky watchers around the world The moon shadowed by the Earth is seen during a total eclipse on February 20, 2007 in Mexico city. Total lunar eclipses occur when the Sun, the Earth and the Moon are all in alignment and the Moon travels into the broad cone of shadow cast by the Earth. The Moon does not become invisible, though, because there is still residual sunlight that is deflected towards it by the Earth's atmosphere, most of which is light in the red part of the spectrum. Getty Images Lunar eclipse delight for sky watchers around the world This file picture taken on February 21, 2008 is combo picture of five images showing various stages of the lunar eclipse as seen in Sofia. Getty Images Lunar eclipse delight for sky watchers around the world The moon is seen partially eclipsed at is rises in cloudy skies over the San Francisco Bay Bridge February 20, 2008 in San Francisco, California. Getty Images Lunar eclipse delight for sky watchers around the world The moon is partly covered in the Earth's shadow during a phase of the lunar eclipse February 20, 2008 in Miami, Florida. Getty Images Lunar eclipse delight for sky watchers around the world This combination picture shows different stages of the moon over the sky of Mexico City during a total lunar eclipse on February 20, 2008. Total lunar eclipses occur when the Sun, the Earth and the Moon are all in alignment and the Moon travels into the broad cone of shadow cast by the Earth. The Moon does not become invisible, though, because there is still residual sunlight that is deflected towards it by the Earth's atmosphere, most of which is light in the red part of the spectrum. Getty Images Lunar eclipse delight for sky watchers around the world A palm tree blows in the breeze as the moon is covered in the Earth's shadow during a phase of the lunar eclipse February 20, 2008 in Miami, Florida. Getty Images Lunar eclipse delight for sky watchers around the world A total lunar eclipse is seen on February 20, 2008 over Panama City, Panama. The Moon turned an eerie shade of red for people in the western hemisphere, recreating the eclipse that saved Christopher Columbus more than five centuries ago. In a lunar eclipse, the Sun, Earth and Moon are directly aligned and the Moon swings into the cone of shadow cast by the Earth. Getty Images Lunar eclipse delight for sky watchers around the world The moon enters and emerges from the earth's shadow during a total eclipse of the moon on February 20, 2008 over in Titusville, Florida in this composite photograph of the stages from partial (L) to total (C) and back to partial (R). Getty Images Lunar eclipse delight for sky watchers around the world The moon appears red during a total lunar eclipse from Mexico City on February 20, 2008. Total lunar eclipses occur when the Sun, the Earth and the Moon are all in alignment and the Moon travels into the broad cone of shadow cast by the Earth. Getty Images

"It's all hands on deck," said U.S. Forest Service ranger Kurt Nelson, who works in the Sawtooth National Forest near the affluent resort of Sun Valley in central Idaho.

The eclipse will arrive on the west coast of the US on 21 August, going on to spread across the country. It will be the first time such an event has been visible at all in the lower 48 states since 1979 – and the first in 99 years that will sweep across the whole country.

The excitement is leading to what is expected to be the biggest movement of people for tourism reasons in history. People are travelling to the US to take in the sight, and even those who live in the country are driving thousands of miles to make sure they see the total eclipse.

Oregon, Idaho and Wyoming are the first three states traversed by the narrow 2,500-mile "path of totality," mostly through rural areas unaccustomed to heavy traffic.

Roads through Idaho's Sawtooth, for example, are likely to see bumper-to-bumper traffic in the days before and during the eclipse, Nelson said.

That has prompted a regional hospital to park a life-flight helicopter nearby in case of a medical emergency. Extra firefighting crews are also on standby.

Months of bone-dry heat have already brought restrictions on campfires and smoking in many Western forests. But authorities see the fire risks ratcheting up with the influx of travelers, few of whom may understand the dangers.

A wildfire in Oregon's Willamette National Forest prompted the closure this month of access to Mount Jefferson, the state's second-highest peak and a would-be destination for those hoping to see the total eclipse, said Kirk Copic, visitor services information assistant for the forest.

On Thursday, a separate blaze 30 miles south near the town of Sisters, Oregon, also in the path of totality, prompted Governor Kate Brown to invoke the state's Emergency Conflagration Act, freeing up additional firefighting resources. She cited the need "to keep community, visitors and property safe" in the run-up to the eclipse.

In Idaho, state police spokesman Tim Marsano warned that first responders there may not be able to help travelers as quickly as in a normal situation, adding, "The 911 system is going to be pushed to its limit."

Nasa jets will chase the total solar eclipse across the US

In the Sawtooth alone, forest rangers expect as many as 30,000 people to inundate an area around the small town of Stanley, home to just 68 year-round residents.

Nelson said the grass has been mowed down in eight eclipse-viewing areas set up for the public, to ensure fire-safe temporary roadside parking.

Smoke from wildfires already burning in Idaho, Oregon, Montana and elsewhere could impair eclipse-viewing for some, but forecasters say smoke conditions, driven largely by wind speeds and direction, will remain uncertain until a day or two before.

The sun will be so high in the sky that smoke should be of little consequence, unless it's extremely thick, said Michael Zeiler, an avowed "eclipse-chaser" who made a 650-mile (1,000- km) drive, to Casper, Wyoming from his home in Santa Fe, New Mexico, in hopes of witnessing his ninth total solar eclipse.

"This will be the most amazing event you have seen in your life," said Zeiler, a member of an American Astronomical Society panel for public guidance.