Reuters/Chennai, India

India deployed hundreds of extra soldiers and relief workers to the flooded city of Chennai on Saturday, as criticism mounted that the government has been slow to respond to the heaviest rains in a century.

The runway at Chennai airport was partly opened after being shut for the past four days, officials said, aiding the relief effort in a disaster that has claimed 280 lives across the state, according to the official death toll.

Large parts of India's fourth largest city were inundated by up to eight feet (2.5 metres) of water after torrential rains on Dec. 1, leaving many residents trapped on rooftops or upper floors without power or communications.

Chennai has boomed as a centre for vehicle factories and IT outsourcing, but trash-filled drains and building on lake beds in the rush to industrialisation and prosperity has made it more prone to flooding.

While the rains have paused, more than half of Chennai's 859 city areas remain under water, officials, said raising the threat of disease and squalor in the flat, coastal city of six million.

"We are asking for more help from the army, the national disaster relief team," said Atulya Mishra relief commissioner of Tamil Nadu of which Chennai is the capital. "It has been a monsoon unlike anything we have seen in history, we need all the help we can get."

Ten columns of the army, about 1,000 soldiers in all, were being flown into the city to add to the nine columns already engaged in relief and rescue work, Mishra said.

The National Disaster Response Force, a specialist federal unit set up to handle emergencies, would send 20 more teams in addition to the 28 already on the ground, making it the force's largest deployment to a flood disaster.

The runway at Chennai airport had been cleared of water and planes that had been stranded for the past five days were being flown out for technical checks at nearby centres such as Bengaluru, officials said.

Passenger flights had not yet started as the airport terminal was waterlogged, and it could be two more days before it was fully operational.

Some communications had been restored following the floods.

Indian test cricketer Ravichandran Ashwin reached his parents in Chennai after he was unable to contact them for a day when telephone networks went down, local media quoted him as saying in Delhi, where he was playing in a match against South Africa.

On the Old Mahabalipuram Road, home to many IT firms, people were still trapped by high floodwaters.

M. Vijaykumar, a deputy director at the Tamil Nadu fire service, said residents in the area were refusing to leave even though the water level had dropped slightly.

"Some have old parents, they don't want to take chance," she said, with many too scared to wade through floodwaters.