The event -- which occurs when the moon passes directly between the Earth and the sun, blocking the sun's light -- illuminated the sky shortly after 5 a.m. EDT.
NASA started livestreaming the spectacle on its website in the early morning.
The eclipse could be seen in northeastern North America and northern regions of Europe and Asia.
NASA had said it would begin around 4 a.m. and end at 9:11 a.m. ET in the northeastern U.S., but time of maximum eclipse varies by location, according to the Farmer's Almanac.
Though the moon blocked some of the sun's light Thursday morning, NASA emphasized on Twitter that it's "never safe to look directly at the Sun," and advised people to wear eclipse glasses or use an indirect viewing method to watch the eclipse.