Eclipse mania gripped North America on Monday as a breathtaking celestial spectacle set to be witnessed by tens of millions of people offered a rare convergence of commercial and scientific opportunities – and an excuse to party.

The Moon's shadow plunged the Pacific coast of Mexico into total darkness at 11.07am local time and will sweep across the United States, before returning to the ocean over Canada's Atlantic coast just under an hour-and-a-half after landfall.

The Mexican beachside resort town of Mazatlan was the first major viewing spot in North America. Thousands of people gathered along the coastal promenade, setting themselves up in deck chairs with eclipse glasses as an orchestra played the "Star Wars" theme.

Lourdes Corro, 43, traveled 10 hours by car to get there.

"The last one I saw was when I was 9 years old," Corro said. "There are a few clouds but we can still see the sun."

Festivals, viewing parties, and even mass weddings are planned along the eclipse's "path of totality," where the Moon will be seen completely obscuring the Sun for up to a few minutes – weather permitting. Cloud cover was forecast over Texas and northeastern US states.

"A total solar eclipse is one of the most emotional events one can experience," Jane Rigby, the senior project scientist for the Webb space telescope, posted. "You're a part of the universe."

This year's path of totality is 185 kilometres wide and home to nearly 32 million Americans, with an additional 150 million living less than 200 miles from the strip. Those further away can still enjoy a partial eclipse, or follow a webcast provided by Nasa.

The next total solar eclipse that can be seen from a large part of North America won't come around until 2044. (AFP/Reuters)