* Heaviest 24-hour downpour in a century
* Torrential rains to continue for three days - forecaster
* Residential areas inundated, factories forced to close
* Chennai airport closed till Dec. 6
* Chennai airport swamped, flights cancelled
* PM Modi cites climate change risks (Adds airport closing until Dec. 6)
By Sandhya Ravishankar
CHENNAI, India, Dec 2 (Reuters) - The heaviest rainfall in over a century caused massive flooding across the Indian state of Tamil Nadu, driving thousands from their homes, shutting auto factories and paralysing the airport in the state capital Chennai.
The national weather office predicted three more days of torrential downpours in the southern state of nearly 70 million people.
“There will be no respite,” Laxman Singh Rathore of the India Meteorological Department told reporters on Wednesday.
No deaths were reported in the latest floods, but since heavy rain set in on Nov. 12 there have been 150 deaths in Tamil Nadu. More than 200 people were critically injured over the past 24 hours in Chennai, a senior home ministry official said.
Prime Minister Narendra Modi has blamed climate change for the deluge, injecting urgency into the debate at global climate talks in Paris and highlighting the vulnerability of tropical nations like India to extreme weather.
Physician Rupam Choudhury said he and a friend had to wade through neck-deep water to reach high ground from where an army truck brought him to his hospital in the heart of Chennai.
Dr. A. Ramachandran’s Diabetes Hospital was running out of oxygen for patients and diesel for power generators, he said by telephone. Most mobile networks were down in the city and food supplies running low.
Chennai, India’s fourth most populous city, is a major auto manufacturing and IT outsourcing hub. Ford Motor, Daimler , Hyundai and Nissan told workers to stay at home, while U.S. listed outsourcing firm Cognizant shut its 11 local offices.
Airlines suspended flights into Chennai’s flooded international airport, causing wider disruption to air travel. Authorities later decided to close the airport until Dec. 6.
“The biggest challenge is to find a way to clear the inundated airport and main roads,” said Anurag Gupta at the National Disaster Management Authority (NDMA) in New Delhi.
Passengers stranded at the airport said they did not know when they would be able to fly, or where to stay if they could not. “All of us here are getting agitated because none of the hotels nearby are vacant. Where do we go?” traveller Vinit Jain told Reuters Television.
In a limited initial relief effort, four helicopters dropped food, water and medicines, while fishing boats commandeered by the military were collecting stranded residents. A major relief effort by 5,000 soldiers was promised within 24 hours.
“The entire state machinery has collapsed. Most officials are forced to sit at home. It’s a very frustrating situation,” said a home ministry official, who requested anonymity because he was not authorised to speak on the record.
Weather experts say the seasonal northeast monsoon was responsible for the flooding in the city of six million, but was amplified this year by El Nino, a warming of the eastern Pacific Ocean that can have far-reaching climate effects.
Tamil Nadu is a major rice and sugar cane producing region, and a senior member of a local farmers’ association said floods had washed out up to four agricultural districts.
Modi has ordered rescue teams and paramilitary forces to launch an extensive relief and rescue operation in Chennai.
He had blamed climate change for the heavy rains that hit the southern state last month, tweeting before attending the UN climate summit in Paris this week: “We are feeling the impact of fast-paced climate change.”
Hundreds of divers and army rescue teams entered inundated homes, taking the injured to hospital. Authorities said more than a million people were affected by the flooding, with some residents bemoaning the slow response of the relief teams.
Social media networks carried many appeals for help, while others offered assistance. Siddarth, a popular Tamil film actor who goes by one name, was coordinating a relief effort on Twitter.
“The police want to help but there are no boats. We are trying not to panic,” said Ramana Goda, who took refuge at a police station after fleeing his home with his family overnight. (Additional reporting by Rupam Jain Nair, Krishna N. Das, Frank Jack Daniel, Nidhi Verma,Manoj Kumar and Mayank Bhardwaj in New Delhi; Sumeet Chatterjee and Clara Ferreira Marques in Mumbai; Writing by Krista Mahr and Douglas Busvine; Editing by Miral Fahmy, Nick Macfie and Mike Collett-White)