Three tons of chemical waste leaked from an illegal processing plant in?Shanghai on Thursday evening, causing air pollution, environmental watchdogs said yesterday.

Shanghai Environmental Protection Bureau said the waste organic solvent came from a chemical plant, which has since been closed down, in suburban Jinshan District.

This follows reports of a foul-smelling gas cloud in nearby Jiaxing City of Zhejiang Province on Thursday night.

The Jiaxing environmental watchdog said this was caused by chlorotoluene, a poisonous material used in making pesticides, medicine and dye products, and that it came from the Shanghai direction.

Shanghai environmental bureau officials said yesterday they are still investigating whether the Jinshan District leak is linked to the reported gas cloud in Jiaxing.

The city watchdog said the plant, which was engaged in organic solvent reclaiming, processing and sales without a license, was closed by the district government.

Its management is being investigated by the district police, environmental and work safety administration authorities.

Officials from Jiaxing Environmental Protection Bureau said on Friday that the smell detected in Jiaxing City between 8pm to 10pm was chlorotoluene.

The bureau said it suspected a chemical plant in Jinshan was responsible, as the leakage position, wind direction, smell and organic materials all tallied in a joint investigation with Shanghai authorities on Thursday night.

Shanghai environmental watchdog said yesterday that there had been a leakage of 3 tons of black oily material from a broken valve of an organic solvent container at Shanghai Chunzhong Chemical Industry Co in Jinshan's Zhangqiao Village about 6pm on Thursday.

The bureau did not confirm the organic solvent was chlorotoluene. It said the authorities will pursue those responsible for setting up the unlicensed business in September last year.

Officials in Jiaxing said it was rare to have reports of a foul-smelling gas over such a large area.

They added that the gas shouldn't cause serious harm as it was low density and didn't last a long time.