Twenty-seven people were hospitalised on Friday after a chlorine leak at a factory in central Russia's Perm region, emergency workers said.
Medical officials said four of the 27 were currently receiving medical treatment, while the rest were under observation in hospital.
The leak occurred early on Friday at a liquid chlorine production factory in Berezniki.
An emergencies ministry official said the situation was under control.
Three people died in Berezniki in November 2012 after a chemical leak at a factory. Investigators said ventilators were not functioning at the factory.
In July 2011, around 30 people were hospitalised after a leak at a non-ferrous metals delivery point in Perm region.