A conservative Indian government estimate puts the death toll from the accident during the past two decades at more than 15,000 people. But activists working for the rights of Bhopal's impoverished residents say the real death toll is twice the figure put out by the Indian government. The human rights watchdog Amnesty International strikes a middle ground, estimating the total death toll is now between 22,000 and 25,000 people.
Indian officials also say 800,000 people now suffer from illnesses linked to the accident.
Vijay Nagaraj is a New Delhi-based consultant for Amnesty and the author of a new Amnesty report on the 20th anniversary of the Bhopal disaster, called "Clouds of Injustice."
In an interview with RFE/RL, Nagaraj accused Union Carbide and its subsequent owner Dow Chemicals of failing to provide full data about all of the chemicals that were released. Nagaraj also criticized the Indian government for prematurely ending a medical enquiry into the consequences of the accident and of failing to keep authoritative records on related deaths.
"As far as Dow-Union Carbide are concerned, they must come and face the criminal trial that is ongoing. They must clean up the pollution that the plant has caused. They must make full reparations to the victims and also release all information pertaining to the toxicology of the gases that were released that night. The government of India must ensure that there is a comprehensive assessment of the exact damages -- including the number of lives lost and the nature and extent of injuries to people. [The Indian government also must] ensure that people get justice. [It must] ensure that there is comprehensive medical, economic, and social rehabilitation and that people are fairly and justly compensated. That's the basic minimum that we expect from the company and from the Indian government," Nagaraj said.
New Delhi and Union Carbide reached an out of court settlement in 1989 under which the U.S. firm paid out $470 million, earmarked for helping victims.
A statement issued by Union Carbide last month says the settlement put an end to "all existing and future claims arising from the incident." It also notes that Union Carbide immediately accepted moral responsibility for the accident. But Nagaraj argues that those payments did not end the firm's legal responsibilities.
What troubles many Bhopal residents is that nearly two-thirds of Union Carbide's $470 million settlement payment still has not been disbursed to the people the money was supposed to help. One of those residents, Ram Prakash Jain, spoke to Reuters.
"Whatever compensation we will get will never be enough because the magnitude of the tragedy was too high. People here are just like zombies. Everyone is suffering from one or another disease. Nothing will help us. I have spent more than 200,000 rupees [about $5,000] for my wife's treatment and got only 25,000 rupees [about $500] in compensation until now," Ram Prakash Jain said.
Bhopal laborer Itwari Lal says no amount of money can compensate for the loss of his son on the night of the tragedy.
"When we heard the gas had leaked, I went to the hospital. It was there that I saw my son die a horrible death," Itwari Lal said.
Activist Abdul Jabbar works with Bhopal survivors who either inhaled the toxic fumes or who have become ill from contamination during the last 20 years.
"People are just dying here. They are in a very bad condition. People are dying due to receiving the wrong treatments. There is no diagnosis. All quacks are now flourishing. People don't have money. Because of constantly falling sick, they are also not able to concentrate on their work," Jabbar said.
The pesticide plant in Bhopal stands boarded and empty today. But activists and independent researchers say it still poses an enormous environmental hazard that is polluting groundwater.
A study commissioned by the environmental group Greenpeace says the site is easily accessible despite a fence, a wall and government security guards. Greenpeace also notes that land at the site is being used for the grazing of livestock and as a playground for children.
BBC correspondent Paul Vickers visited Bhopal last month and reported that the smell of chemicals still hangs in the air. Vickers documented numerous aging chemical tanks on the site -- many with holes rusted through and chemicals spilling onto the soil.
Vickers also took a sample from a well near the plant that residents use for drinking water. A laboratory in the United Kingdom later found levels of contamination that were 500 times higher than the maximum limits recommended by the World Health Organization.
But those findings have been challenged by the chief of the local government's pollution control board, P.S. Dubey. He admits that the municipal government's own tests have found contamination. But he says the levels are not as high as the BBC has reported.
Uma Shankar Gupta -- the minister in charge of providing relief to the victims of Bhopal -- says there is still "some amount" of toxic waste at the site. Gupta also confirms that there is some water contamination. But he says the exact reasons for the polluted groundwater are not known.
Gupta says a survey of the plant is now being conducted as the first step in a renewed effort to clean up the site.
(Reuters contributed to this report.)