Bhopal gas tragedy survivor and gas victims hold posters and shout anti-govenment slogans at the district court as they wait for the verdict in Bhopal, Madhya Pradesh

Partially blind gas victim waits for the verdict with other victims in the premises of Bhopal court

Seven people have been convicted of 'death by negligence' over the Bhopal gas tragedy in India that killed 15,000 people more than 25 years ago.

The former chemical company executives, many of them in their 70s, were convicted alongside their U.S. firm Union Carbide India Ltd - which no longer exists - and face up to two years in prison.

The convictions are the first since the disaster at the Union Carbide plant, the world's worst industrial accident.

On December 3, 1984, a pesticide plant run by the subsidiary of Union Carbide leaked about 40 tons of deadly methyl isocyanate gas into the air in Bhopal, central India, quickly killing about 4,000 people.

The lingering effects of the poison raised the death toll to about 15,000 over the next few years.

Activists insist the real numbers are almost twice that, and say the company and government have failed to clean up toxic chemicals at the plant, which closed after the accident.

The verdicts, which were handed down in a local court and are likely to be appealed, came as the case crawled through India's notoriously slow and ineffective judicial system.

A crowd watches as a man pastes identification labels onto dead children's foreheads, killed in the December 1984 Bhopal Gas tragedy

A woman and her child lie dead on a street on December 3, 1984, after the toxic gas leak. The acciden killed thousands and contaminated water and soil when toxic methyl isocyanate gas leaked from Union Carbide's pesticide plant

India's Central Bureau of Investigation, the country's top investigative agency, had originally accused 12 defendants: eight senior Indian company officials; Warren Anderson, the head of Union Carbide  at the time of the gas leak; the company itself and two subsidiary companies.

Seven of the eight Indian company officials were convicted today. The other one has since died.

Anderson and Union Carbide have never appeared in court proceedings.

Union Carbide was bought by Dow Chemical in 2001. Dow says the legal case was resolved in 1989 when Union Carbide settled with the Indian government for $470million, and that all responsibility for the factory now rests with the government of the state of Madhya Pradesh, which now owns the site.

Last July, the same court in Bhopal had issued a warrant for Anderson's arrest and also ordered the Indian government to press Washington for his extradition.

The Union Carbine plant in Bhopal, 25 years after the deadly gas leak

Anderson was briefly detained immediately after the disaster, but he quickly left the country and now lives in New York. It was not immediately clear if the Indian government had begun to process the Bhopal court's request.

Extradition proceedings are usually mired in a complex tangle of legal paperwork and can take years to complete.

Investigators say the accident occurred when water entered a sealed tank containing the highly reactive gas, causing pressure in the tank to rise too high.

Union Carbide said the accident was an act of sabotage by a disgruntled employee who was never identified.

It has denied the disaster was the result of lax safety standards or faulty plant design, as claimed by some activists.

The Central Bureau of Investigation said the plant had not been following proper safety procedures.