(Adds airport status, power and telecoms slowly back on, paragraphs 3, 11-13)
By Sanjeev Miglani and Sandhya Ravishankar
CHENNAI, India, Dec 5 (Reuters) - India deployed hundreds of extra soldiers and relief workers to the flooded city of Chennai on Saturday, as residents said the government has been too slow to respond to the havoc wrought by the heaviest rains in a century.
About 280 people have died across Tamil Nadu state since it was hit by torrential rains on Dec. 1 that left large sections of capital Chennai under up to eight feet (2.5 metres) of water, and trapped people on rooftops with no communication.
Although the rains had stopped and Chennai's airport had partially reopened, more than half of the city was still flooded and some residents trapped on rooftops, too scared to wade through the water, officials said.
"Some have old parents, they don't want to take chance," said M. Vijaykumar, deputy director of Tamil Nadu Fire Service.
Residents say the city authorities gave no warning that they were going to open overflowing reservoirs into the Adyar river, which led to sharp rise in water levels.
Vikram Kapur, a commissioner of the Chennai Corporation, a government body that administers the city, said that employees had gone to forewarn residents when the reservoir was opened up.
"The local corporation official, the water works officer and the police are given instructions to inform the public," Kapur said.
In Jafferkjanpet and Vellachery, two of Chennai's worst affected areas, some said the authorities had only just showed up with food packets.
"We have had no power, no milk for the children," said M.A. Sheikh, accusing the government and media were giving a false picture of the relief effort. When Prime Minister Narendra Modi visited the city this week he announced 10 million Indian rupees ($150,000) of extra assistance for relief operations.
Late on Friday, Tamil Nadu's most senior state official, K. Gnanadesikan, and other top colleagues appeared before reporters for the first time since the flooding and defended the aid operation, saying those involved were doing an "extraordinary job under trying circumstances."
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.
Ten columns of the army, about 1,000 soldiers in all, were being flown into the city to add to the nine columns already on the ground, said Atulya Mishra, relief commissioner for Tamil Nadu state.
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, Mishra said. Each team has about 40 members.
"It has been a monsoon unlike anything we have seen in history, we need all the help we can get," he said.
The runway at Chennai airport was partly reopened on Saturday after four days of being shut, and 34 passenger planes that had been stranded there were being flown out for technical checks at nearby centres such as Bengaluru, officials said.
Passenger flights to and from Chennai, India's fourth largest city, will resume at 0600 hours local time on Dec. 6, the federal government said in a statement late on Saturday, but only day flights for the time being.
Six out of seven power stations in Chennai that were flooded were functioning, but one was accessible only by boat and would require time before starting up again, state officials said.
Telecoms remained a problem with cell towers damaged, the federal government said in a statement, though some communications had been restored in recent days.
$1 = 66.6330 Indian rupees Additional reporting by Suvashree Choudhury in MUMBAI and Rachel Chitra in BENGALURU; Editing by Richard Pullin and Raissa Kasolowsky