At least 30 people have been taken to hospital after a toxic chemical leak in the city of Chelyabinsk in Russia's Ural mountains, say officials.

Thousands more suffered breathing difficulties after containers of the toxic element bromine were broken while in transit.

Bromine can damage internal organs and the nervous system.

Officials said there had been a breach in safety regulations and have launched an investigation.

Russia's Interfax news agency said the bromine was being carried by train in 2,267 two-litre (four-pint) glass containers, some of which were broken as carriages were moved around at the town's main railway station.

Between 24 and 50 litres (5-11 gallons) were released, said officials. NTV broadcast images of a dirty orange cloud hanging over the town and said there had been a run on face masks.

"It's impossible to breathe," one resident told reporters.

Interfax said 113 people had sought medical help and 33 had been admitted to hospital. Some schools sent their students home and people were advised to stay indoors.

But officials have said there is no need for alarm and that the leak was under control.

"To calm down the population, I wanted to say that bromine is used for medical purposes to sedate people. Albeit not in such quantities, of course," said Alexander Galichin, the region's minister of radiation and ecological security.

The Urals transport authority said there had been a "breach of the regulations on handling, transporting and storing chemical substances".

The prosecutor-general's office has ordered the regional authorities to identify those responsible and "take prosecution response measures if there are grounds for doing so".

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