US President Donald Trump has risked sustaining eye damage after ignoring NASA experts' advice and looking directly at a solar eclipse.

Parts of the US experienced a total eclipse as the line of darkness raced 4200 kilometres across the continent in about 90 minutes on Monday.

NASA experts warned that anyone who looks at the eclipse without specially designed sunglasses can damage their retina within 20 seconds.

Despite this, President Trump was photographed directly looking at the natural phenomenon.

According to CNN, while onlookers in the crowd below shouted 'Don't look!' the president looked up at the once-in-a-century event.

President Trump subsequently put on the glasses yet the image of him looking at the sun was widely shared on social media.

The US Midwest to South Carolina was totally bathed in darkness for a few minutes, while other parts of the US experienced a partial eclipse.