NEW DELHI (AFP) - Protesters in the Indian city of Bhopal on Tuesday burned effigies representing US conglomerate Dow Chemicals and displayed placards demanding justice as they marked the 30th anniversary of the world's deadliest industrial disaster.

Some held old black and white photographs of loved ones lost on the night of December 2, 1984, when a cloud of highly toxic methyl isocyanate gas spewed from a Union Carbide factory in Bhopal and blew across the city.

More than 3,500 people were killed in the immediate aftermath and as many as 25,000 are estimated to have died in the years that followed.

Many of those who were exposed to the gas have given birth to physically and mentally disabled children.

For decades, survivors have been fighting to have the site cleaned up, but they say the efforts were slowed when Dow Chemical took over Union Carbide in 2001.

"We want justice," read one placard featuring the chilling photograph of a hand scraping earth from the head of a partially buried dead baby, the best-known image of the disaster.

"Dow shall assume liabilities for the continuing disaster in Bhopal," read another.

Activist groups have long demanded that Dow award additional compensation to the victims and clean up the accident site, which they say is still contaminated.

Residents also opened Remember Bhopal, an oral history museum that houses photographs and the personal belongings of the victims, accompanied by audio clips recorded by relatives.

Survivors have recorded their own harrowing testimony for the museum.