A Finnish beach has been covered by an unusual expanse of egg-shaped chunks of ice.

Risto Mattila, an amateur photographer, posted the image on Instagram with the caption “snow ball sea” after coming across the scene on Hailuoto Island.

“I was with my wife at Marjaniemi beach. The weather was sunny, about -1C and it was quite a windy day,” he told the BBC.

“There we found this amazing phenomenon. There was snow and ice eggs along the beach near the water line.”

It is “really rare” to get the mixture of geographical and meteorological conditions necessary to form these ice balls, Patrick Erikkson, an ice expert at the Finnish Meteorological Institute, told The Independent.

Winter snow around the world Show all 11 1 /11 Winter snow around the world Winter snow around the world South Korea Tourists view snow-covered trees on Jeju Island, South Korea. EPA Winter snow around the world Finland People walk through snow-covered streets in the city of Outokumpu, Finland, amid a heavy winter storm. EPA Winter snow around the world Paris A newly wed couple pose for photographs as snow falls over Paris on 22 January 2019. LIONEL BONAVENTURE/AFP/Getty Images Winter snow around the world Lebanon The snow-covered town of Bcharre that flanks the Unesco World Heritage Site of Qadisha in the Lebanese mountains north of Beirut, 1,450m above sea level. JOSEPH EID/AFP/Getty Images Winter snow around the world Saint-Aubin, France A French farmer walks under the snow in Saint-Aubin, northern France, with "Imminence", the mascot "Bleue du Nord" cow at the 2019 International Agriculture Fair in Paris on 22 January 2019. FRANCOIS LO PRESTI/AFP/Getty Images Winter snow around the world New York State Pine trees blanketed in snow after Storm Harper swept through the southern tier of western New York State. Flickr/ryanhallock Winter snow around the world Netherlands The first snow of the year fell across the Netherlands on 22 January 2019. EPA/KOEN VAN WEEL Winter snow around the world Paris A man takes a picture in the Tuileries garden as snow blankets Paris on 22 January 2019. LIONEL BONAVENTURE/AFP/Getty Images Winter snow around the world Germany A no trespassing sign stands in the snow at the train station in Berchtesgaden, Germany. Reuters Winter snow around the world Nepal A woman tries to catch snowflakes on her tongue in Chandragiri Hills in Kathmandu, Nepal, on 23 January 2019. Reuters Winter snow around the world Siberia Fishermen walk along the frozen Yenisei river in the Siberian taiga area outside Krasnoyarsk, Russia, in temperatures of -26C. Reuters

He explained when sea water is cooled down to freezing point, ice crystals can form near the surface and join together to form a sheet in deep water.

“If we are closer to shore, then these lumps start to roll,” Mr Erikkson said.

“When we have water and very cold air, they start growing and collecting more and more ice around them. They can get as big as footballs that way, rolling around in the shore line.”

Mr Mattilla, the photographer who stumbled across the ice balls on the beach, said the smallest ones were the size of eggs, while the largest were as big as footballs.

“That was an amazing view. I have never seen anything like this during 25 years living in the vicinity,” he told the BBC.

Mr Erikkson said: “You really need to find the right conditions for this to happen."

He said the “natural phenomenon” requires “a situation where the water has cooled down, a sea area in the right stage of freezing, the wind from a suitable direction generating the wave motion from the shore line and a shallow, smooth sea floor”.