Disabled children suffering the effects of the 1984 Bhopal disaster in India are to take part in a "Special Olympics" on Thursday to protest against London 2012 sponsor Dow Chemical.

The event is aimed at raising awareness about the legacy of birth defects and pollution from the accident at a factory owned by US chemical company Union Carbide, which was bought by Dow in 1999, organisers said Tuesday.

The plant leaked poisonous gas into neighbouring slums in Bhopal, killing thousands instantly and tens of thousands more over the following years in the world's worst industrial accident.

The "Bhopal Special Olympics" will see at least 100 physically and mentally disabled children compete on a sports field in the shadow of the defunct factory, which still contains toxic waste left untreated by local authorities.

The contests in Bhopal -- the day before the London Games officially open -- will include football, an "assisted walk" and a "crab walk", in which participants unable to stand on two feet race on their hands.

"We are doing this mostly due to Dow's attempt to greenwash its crimes," Rachna Dhingra, a spokeswoman for the five survivors' groups behind the initiative, told AFP.

"We all find it ironic that a corporation that has disabled people in Bhopal is sponsoring the Olympic Games."

Organisers are also targeting Britain and its colonial crimes, particularly in India. The Bhopal Olympics "will open with songs and dances focusing on matters that British people could be ashamed of," Dhingra said.

The decision by London 2012 organisers to stick by Dow Chemical has caused anger in Bhopal and led to complaints from the Indian government, which asked for the company to be dropped as a sponsor.

"Our biggest qualm with (British Prime Minister) David Cameron and (chief Olympics organiser) Lord Sebastian Coe is the simple reason that they never gave the survivors of Bhopal the chance to express themselves," Dhingra said.

Dow bought Union Carbide more than a decade and half after the disaster and insists all liabilities were settled in a 1989 compensation deal that saw Union Carbide pay the Indian government $470 million.

The local and federal governments have also faced criticism in India for failing to clear the site and prevent further contamination of groundwater more than 25 years after the disaster.

Dhingra said the children in the Bhopal event were all willing participants.

"I would say 60 percent (of the children) have had training. This is part of their rehabilitation," she said.

"This is what Dow has done. There is no better way to show their crimes."

The organisers of the London Olympics and the International Olympic Committee have faced consistent questions over their choice of sponsors, including fast-food giant McDonalds and soft drink maker Coca-Cola.

After an outcry in India and speculation about a boycott by Indian athletes, London organising officials said Dow's branding would not appear on a giant fabric wrap around the main stadium in the east of the British capital.