At least 10 children and an adult have died after boats they were in capsized in stormy weather during an outing on a lake in the Republic of Karelia in north-west Russia, police said on Sunday.

"We have found 11 corpses, of which 10 are children. Three people are still unaccounted for," a police officer said.

He added that two of the three boats that were being used capsized in Syamorzero lake because of the bad weather.

Local media reports said that around 50 people, mostly children aged 12 to 15, were on the boat trip.

The mayor of Moscow Sergei Sobyanin wrote on his Twitter account that, according to preliminary information, around 10 children from Moscow had died.