Citizens were baffled when blue snow covered the ground in St Petersburg, Russia.

The odd phenomenon was captured on video after the coloured snow fell this week on the city in Leningrad Oblast, President Vladimir Putin's hometown.

Residents were shocked at the incident and became worried it could have been due to toxic chemicals in the atmosphere.

The odd phenomenon was witnessed in Leningrad Oblast, President Vladimir Putin's hometown

Some believe the blue snow was a result of the demolition of the city's chemical-pharmaceutical research institute

Samples were taken to a laboratory for analysis and an investigation into the incident has been launched

Some believed the snow was a result of the demolition of the city's chemical-pharmaceutical research institute.

According to local media, experts said the colours could have been caused by cobalt, a metallic element, or methylene blue, a substance used in some medical treatments.

Samples were taken to a laboratory for analysis and an investigation into the incident has been launched.

In February 2015, blue snow also occurred in the Russian city of Chelyabinsk, some 1,500 miles to the east of St Petersburg.

An investigation was carried out which revealed that the blue colour was due to food colouring used in Easter eggs.

The dye had got into the ventilation system of a factory and been spread all over the area.

It is not clear yet exactly why the latest blue snow has fallen.

But after an average of 1 centimetre (0.39 inches) fell, citizens have been simply shovelling the phenomenon out of the way to go about their daily lives.