The moon completely blocked out the sun's rays on Monday in a rare solar eclipse across North America that created and eerie darkness over much of the United States.

The total eclipse, centred in a 100-kilometre-wide band stretching across 14 states, was first visible in the US in Madras, Oregon, starting at 10:19 am (1719 GMT) and lasting for about two minutes, NASA said in a statement quoted by dpa.

The temperature dropped by a couple degrees and the corona, the outermost part of the sun's atmosphere, was visible as a glowing ring.

The moon is passing between the sun and the Earth in a rare alignment that last occurred in the United States in 1979. It will cross the continental United States over a span of almost two hours ending in South Carolina at 4:06 pm (2006 GMT).

The event, which has excited everyone from professional astronomers at NASA to schoolchildren across the country, is the first coast-to-coast solar eclipse in the US since 1918.

While Monday's eclipse was to darken the day at least partially across the US, and to a lesser extent in Canada and Mexico, much of the excitement was centred on the so-called path of totality, where the moon blocked out the sun completely.

Millions of people have gathered in cities and towns near the path in order to experience the total eclipse, which has been described as peaceful, spiritual, exhilarating and shocking.

Astronomers have encouraged people who really want to experience it to get to the path of totality. Traffic problems were reported days before the eclipse in some areas near the path.

Although Washington does not lie in the path, a White House official said US President Donald Trump will watch the total eclipse from the south-facing balcony of the White House with First Lady Melania.

The US labour department expects the eclipse to cost about 700 million dollars due to diminished productivity, because people will spend time talking about the solar eclipse, reading about it or leaving their desks and venturing outside to see it, according to numbers released by human resources firm Challenger Gray.

Experiencing a total solar eclipse happens about once in 375 years in any given location, according to NASA.

People have been warned not to look directly at the eclipse even if they are in an area where the sun will be only partially obscured. NASA and other US agencies have issued special-purpose solar filter glasses and supplied instructions on how to make a safe hand-held solar viewer.