Friday's rally followed an overnight candlelit vigil

Thousands died on 3 December, 1984, and in subsequent years after the leak at the Union Carbide chemical plant.

Hundreds of survivors, relatives of the dead and rights activists marched through Bhopal demanding justice.

However, despite a public holiday in the city, correspondents say that life carried on as normal for many people.

'Betrayed'

"We will burn effigies of Union Carbide and Dow Chemical to voice our protests," Rashida Bee, a survivor who heads a women victims' group, told the Associated Press news agency.

"These two companies have betrayed the victims of Bhopal."

Lethal chemicals are still lying around at the plant, some in the open Rashida Bee, women victims' group In pictures: Tragedy remembered Indian press anger Bhopal's forgotten hero

Union Carbide is now a subsidiary of US firm Dow Chemical. The government of Madhya Pradesh state took over running the site in 1998.

Mrs Bee said protesters would keep fighting until the victims' demands for compensation, medical care and rehabilitation were met.

"Lethal chemicals are still lying around at the plant, some in the open. Every time it rains these poisonous chemicals are leaked into the soil, affecting groundwater resources in the area," she said.

Condolence meetings

Protesters marched in Bhopal on Friday shouting "Don't forget the victims of the genocide in Bhopal!", "Death to Dow!" and "We will fight, we will win!".

BHOPAL'S DEATH TOLL Official figures on initial deaths: nearly 3,000 And subsequent deaths: nearly 15,000 And permanent disabilities: 50,000 Unofficial figures on initial deaths: 7,000-8,000 And subsequent deaths: 15,000-20,000 Compensation: Union Carbide agree to pay $470m in 1989 Official source: Indian Council of Medical Research

Banners accused Union Carbide and Dow Chemical of failing to provide adequate compensation and medical help for victims.

However, the BBC's Faisal Mohammad Ali in Bhopal says the crowds of protesters were small.

Not everyone was aware of the protests he says, with some people speaking of cynicism about the chances of ever getting justice for what happened.

Union Carbide argues that it has provided substantial funds in compensation and done much work to help the victims and improve the environment in Bhopal.

It says groundwater tests around the plant in 1998 indicated it was free of toxins and that the water contamination was the result of improper drainage and other pollution.

On Thursday the state government announced a new survey to determine the extent of contamination, although this has not been confirmed by the central government in Delhi.

A number of condolence meetings remembering the victims were held on Friday.

Compensation concerns

Overnight about 300 people held a candlelit vigil outside the derelict factory to remember the dead.

The mood was mostly sombre though angry widows marched to the plant crying "Death to Union Carbide!".

Debate still rages on how toxic the abandoned site remains

Shortly after midnight 20 years ago, 40 tonnes of highly poisonous methyl isocyanate gas escaped in the capital of Madhya Pradesh.

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.

The Indian government is awaiting the outcome of a US court hearing on whether Dow Chemicals should be asked to clean up the site further.

The protesters also want to highlight their concerns that only a part of compensation paid by Union Carbide - worth almost $500m - has reached the victims.