Relatives of those killed by the Bhopal toxic gas leak in India have gathered, 20 years later, at the scene of the world's worst industrial accident.
Thousands of people lost relatives to the disaster
Thousands died on 3 December, 1984, and for years after the leak at Union Carbide's chemical plant in the city.
About 300 people held a candlelit vigil outside the derelict factory ahead of a rally on Friday.
The mood was mostly sombre, though angry widows marched to the plant crying "Death to Union Carbide!".
They demanded the imprisonment of Warren Anderson, the former chairman of the US firm, who still faces manslaughter charges but has never been brought before the Indian courts.
Local people and activists complain that the site of the accident is still swimming in toxic chemicals, and say people are still suffering poisoning effects.
On Thursday the state government announced a survey to determine the extent of contamination.
It will be a "first step" to a clean-up, state minister Uma Shankar Gupta told the AFP news agency.
The response from environmental activists was terse.
"This is the slowest first step in history," said Vinuta Gopal of Greenpeace India.
One of those at the plant on Thursday was Musharraf Ali, 51, whose wife Afroze died of blood cancer in 1996.
"Doctors told my wife and myself that she had blood cancer in 1993 and within three years she was gone," Mr Ali said.
"I come here for the vigil every year to express my sorrow at the horrific accident that destroyed my life."
People fled from the poison gas in the middle of the night
Many protesters were from elsewhere in India or overseas, and said they wanted to show their solidarity with people in Bhopal.
Shortly after midnight 20 years ago, 40 tonnes of highly poisonous methyl isocyanate gas escaped in the capital of Madhya Pradesh state.
According to official figures, nearly 3,000 people died on the night of the disaster as gas seeped from the plant, and there have been nearly 15,000 deaths related to the accident.
Campaign groups put the figures much higher.
Many local people still suffer respiratory and other illnesses and say their water supplies are still contaminated.
The federal government has asked the Engineers India Limited company to carry out a survey of the site to assess the extent of the problem, said Mr Gupta, the state minister.
However, there has been no confirmation from the central government in Delhi that the survey will take place.
A spokeswoman for the engineering company told the BBC: "We still have not been awarded any such survey work in Bhopal."
The Indian government is awaiting the outcome of a US court hearing on whether Dow Chemicals, which took over the plant from its subsidiary Union Carbide, should be asked to clean up the site.
The now-disused site is littered with toxic waste
The BBC's Nick Bryant in Bhopal says that 20 years after the incident, the plant continues to be an environmental disaster zone, strewn with an estimated 25,000 tonnes of toxic waste.
In warehouses at the site, broken bags of poisonous materials litter the floor, while deposits of mercury slip across its rusting girders.
Though the site is closed to the public, children often manage to evade the security guards and at one contaminated warehouse building young men have daubed the names of their sweethearts on the walls, our correspondent says.