When Champa Devi Shukla's granddaughter was born with a raft of facial deformities in the Indian city of Bhopal, she was not left short of advice.

"Many people said you should kill her. They said she is of no use, you should stuff tobacco in her mouth" to suffocate her, said Devi Shukla.

"But I thought, I'm not going to let her die. I've already lost three sons to this tragedy so I'm not going to lose someone else."

When a cloud of highly toxic methyl isocyanate (MIC) gas blew across Bhopal on the night of December 2, 1984, around 3,500 people were killed in the immediate aftermath and up to 25,000 are estimated to have died in the long-run.

The tragedy didn't end there for locals living around the Union Carbide chemical plant at the centre of the disaster, with many later giving birth to children with abnormalities.

While the exact numbers are impossible to pin down, the streets near the now abandoned factory are full of families whose children born post-1984 have either died prematurely or have major health problems.

But the government has not confirmed a link, which would have major implications in terms of compensation so far limited to people who were alive at the time of the world's deadliest industrial disaster.

Devi Shukla lost her husband and three sons on the night. One of her daughters, Vidya, was also left partially paralysed after inhaling fumes, although her condition improved after extensive physiotherapy.

The family was overjoyed when Vidya fell pregnant, but more pain was to come. Her first child, a son called Sushil, was stunted and is now less than four feet tall at the age of 18.

A second son, Sanjay, died after five months. And then Vidya gave birth to a daughter, Sapna.

"She was born with a cleft lip and palate. She has had three lots of operations so far" with one still to go to reconstruct her nose, Devi Shukla told AFP.

Sapna, now a happy 13-year-old, says she wants to become a doctor when she is older.

Her own family's experience having convinced her of the link, Devi Shukla helped set up a clinic for children of survivors who have health problems.

The Chingari Trust has 705 pupils, many with conditions such as autism or deafness. The centre provides physical and speech therapy along with schooling and sports.

- 'Poisoned water' -

Rasheda Bee, a co-trustee, says she believes most of the illnesses stem from "drinking poisonous water".

Her determination to help began after she saw her sister and then her three nieces die of respiratory illnesses.

It was fuelled by a trip to Japan, where she met children of victims of the 1945 Hiroshima nuclear bombing.

Although she is not a doctor, she was involved in tests on the breast milk of 20 mothers. Half were from neighbourhoods close to the factory and the others were on the other side of town.

"The figures for one half were normal but nine out of the 10 living near the plant had high levels of mercury in their milk," she said. Mercury stunts the development of foetuses.

A report a decade ago in the Journal of American Medical Association found boys born to families exposed to the gas were on average 3.9 centimetres shorter than those from other parts of the city.

The head of Amnesty International, which is campaigning for more compensation, says there is clear evidence of poisoning.

"We are now dealing with inter-generational health problems which are being passed on from the parents to the next generation," Salil Shetty told AFP while attending commemorations for the 30th anniversary of the disaster.

"There have been multiple studies over the years... It's very clear that water contamination has happened," said Shetty, adding some water and soil contamination from the plant happened even before the gas leak.

Devi Shukla said even now pupils "have a fear of the drinking water", although the pipes have been changed.

A doctor at a government-funded institute which has been studying child health in Bhopal says it is too early to draw a link between the plant and congenital illnesses.

"It has not been established, but it has not been denied either," the doctor told AFP on condition of anonymity.

Shetty acknowledged the exact cause of some illnesses was contested, but said the onus was on the government.

"Why can't the government of India conduct proper medical research and study? It's not like India doesn't have the capacity to do this. Thirty years is too long for the victims to wait."