Cloud is forecast in places such as Texas, Oklahoma and southern Arkansas as people gather for what's set to be the most viewed eclipse ever.

"A few tornadoes" and "very large hail" are also possible around the time of the eclipse in those states, says the US National Weather Service.

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However it's a different story in the New England region and parts of Canada, where clear skies are set to bring near-perfect viewing conditions.

The eclipse begins on Mexico's Pacific coast around 11.07am local time (7.07pm UK time) before moving into Texas 20 minutes later and tracking northeast.

Some 31 million people are within the 115-mile-wide path of totality - where the sun will be covered by the moon's shadow for an eerie few minutes that will resemble dusk.

Many more 'eclipse chasers' have travelled for the spectacle, paying big money for accommodation months in advance - with some relocating as the forecast shifts.

Others are holding 'eclipse parties', while a million are expected at Niagara Falls - with a state of emergency declared on the Canadian side to free up more resources.

In Fredericksburg, Texas, people who paid $800 for hotel rooms have been looking to offload them due to the murky weather outlook, reports Sky's US correspondent Martha Kelner.

But states like Vermont, which is expecting ideal viewing conditions, is expecting a last-minute influx.

"We're hearing of people potentially rerouting private plane routes to see the eclipse here instead," said Michael Hibben, director of the Pierson Library in Shelburne.

Other US states outside the path of totality will still be able to see a partial eclipse.

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Astronomers also say northern and western parts of the UK will get a "small grazing" of the eclipse between 7.52pm and 8.51pm.

The best spots will be Belfast, where 28.1% coverage of the sun is predicted, and Stornoway in the Outer Hebrides - with a 33.7% eclipse.

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Glasgow is also expecting 12%, Dublin 15%, and Liverpool a tiny 3.1%.

A partial eclipse will be viewed across nearly all of the UK in 2026, but a full one won't happen until 2081 in the Channel Islands or 2090 in the South West.