Millions of Americans gazed in wonder through telescopes, cameras and disposable protective glasses Monday as the moon blotted out the sun in the first full-blown solar eclipse to sweep the United States from coast to coast in nearly a century.

It promised to be the most observed and photographed eclipse in history, with many Americans staking out prime viewing spots and settling onto blankets and lawn chairs to watch, especially along the path of totality the line of deep shadow created when the sun is completely obscured except for the delicate ring of light known as the corona.

The shadow, a corridor just 96 to 113 kilometres wide, came ashore in Oregon and then began travelling diagonally across the heartland to South Carolina, with darkness from the totality lasting only around two to three minutes in any one spot.

The rest of North America was treated to a partial eclipse, as were Central American and the top of South America.

The next total solar eclipse in the US will be in 2024. The next coast-to-coast one will not be until 2045.