Residents in India's southern Tamil Nadu state Saturday were grappling with the aftermath of devastating floods as authorities stepped up relief work following the worst deluge in decades that killed over 250 people.

Thousands of people in Chennai took to the mud-filled streets to buy essentials as authorities worked to restore communication and road networks after Tuesday's record rains worsened weeks of flooding, leaving hundreds of thousands of residents marooned in the state capital.

Residents jostled at grocery stores, petrol stations and cash machines, with the city reeling under a severe shortage of supplies, including drinking water, after the rains finally stopped on Thursday.

"I had to wait almost three hours at the petrol station with more than 200 people trying to get fuel," local resident V Prabhakaran told AFP, adding filling stations have started rationing petrol.

Mobile communication services were badly hit by damage to power infrastructure and a shortage of fuel. The authorities said shortages of essential goods will start to ease as road and rail links are restored and dozens of special trains were running to bring in relief material.

Chennai's international airport was opened for relief flights, four days after planes and the runway were submerged. Officials hope commercial services will resume Sunday.

Hundreds of flood-hit cars and motorcycles remained piled up in the streets of Chennai, which were coated with a thick layer of mud.

Thousands of people were rescued earlier in the week in a massive operation by the Indian army and disaster management teams. Residents were plucked from the rooftops of their marooned homes by helicopters and boats following the devastating floods which officials said were caused by the worst rains in a century.

Rekha Nambiar, National Disaster Response Force (NDRF), who is leading a relief team of more than 1,800 men in the state, said crews were carrying out relief work after flood waters started receding, with the focus on potable water.

"Rescue work is over. We are focused on relief now. We are trying to shift men and machinery to provide drinking water in the affected areas," Nambiar told AFP.

She said teams were cleaning up residential areas to avoid a disease outbreak as authorities distributed water purifying chlorine tablets.

"Right now people are in dire need of food, water and sanitation," she said.

Forecasters expect dry weather next week, ending a long spell of torrential rain.

Experts blamed poor urban planning for the devastation in India's fourth-largest city, home to nearly 4.6 million people, which has grown rapidly in the last few decades to become a major IT and automobile hub.