People in Russian capital Moscow were today urged to stay indoors after an acrid cloud smelling of rotten eggs engulfed the city.

The air 'reeked of sulphide' including over Red Square but experts said they were struggling to understand its source or cause.

One unconfirmed theory was that an industrial plant had leaked a cloud of Styrene over Moscow.

A housewife posted this shocking video from her high rise apartment block, stating: 'This is the horror we are witnessing today.

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Foul: People in Moscow were told to stay indoors after an acrid cloud smelling of rotten eggs engulfed the city

One unconfirmed theory was that an industrial plant had leaked a cloud of Styrene over the city

Contrast: The cloud of fog engulfed a vast portion of Moscow. Pictured, what the city looks like normally

'We can't even see the sun, let alone the playground.

'This is the video from another window - nothing at all is visible, not the forest, nor the neighbouring district.'

She continued: 'This is a kindergarten.' It was closer and visible through the noxious fog.

'Something horrible is going on here,' she said.

'They decided to poison us all.'

The Russian Emergencies Ministry recommended Muscovites to stay indoors while experts tried to understand the cause.

'We suggest people in the capital minimise time they spend outside, and keep windows and doors shut,' said a warning.

Alexander Drobyshevsky, the Ministry's spokesman, said: 'Specialists are taking air tests all around the city. As soon as we have results, we will let you know,'

Major news outlet gazeta.ru warned: 'An acrid fog covers Moscow. A strong hydrogen sulphide emission recorded in the Russian capital.'

The stench was reported to be coming from eastern districts of Moscow, where a strong emission of pollutants was recorded on Monday.

From early morning dozens of phone calls were made to an environmental hotline.

Russian Meteorological Station experts confirmed a sulphide emission in the area of Lyublino.

'We can only record a several times higher concentration of sulphide in the air. We can't yet explain reasons for the emission,' said a spokesman.

Another highly concentrated 'poisonous cloud' covered the Kozhukhovo area of eastern Moscow.

Horror: A housewife who posted a shocking video said: 'This is the horror we are witnessing today'

'It was sunny until 9am, the sky was clear. After 9am a strange fog covered the whole area,' said Irina Chichkina of ecological movement 'Green Kozhykhovo'.

'I've never seen a fog like this.

'There is also a smell, similar to sulphide.'

In Kozhukhovo, a monitoring station showed doubled the normal concentration of toxic styrene in the area.

A local man called Alexander Demenko posted on his Facebook from a locality of Moscow badly his by the 'pollution': 'Styrene affects the peripheral nervous system, the haematopoietic system and even the female reproductive organs.

'There are 80,000 people living in the area, my wife and two children among them.

'Today for me and my family it is a day of survival in the clearest sense of this word.'

She added that nothing at all was visible, including a nearby forest or the neighbouring district