Here's why a mesmerising giant rotating ice disc has formed on a Maine river

A curious formation attracting attention in the US is actually a spinning ice disc that is roughly 91 metres wide.

The formation in the Presumpscot River in Greater Portland has drawn comparisons to an alien spacecraft, a carousel and the moon.

The oddity in Westbrook drew a crowd that stood mesmerised by the slow-turning disc.

The ice formation is believed to have formed naturally in a part of the river where there is a circular current that creates a whirlpool effect, said Tina Radel, the city’s marketing and communications manager.

Locals said they have seen smaller ice discs before but nothing like this one, Ms Radel said.

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Rob Mitchell, who owns a nearby office building, spotted the alien-looking disc and immediately notified the city.

Officials said the disc is spinning slowly counter-clockwise and has served as a big raft for ducks and other birds.

“The ducks were rotating on this big Lazy Susan,” Mr Mitchell said.