The Intensive Care Unit of a hospital is seen flooded and abandoned in Chennai, in the southern Indian state of Tamil Nadu on Friday, Dec. 4, 2015

Severe floods that have hit the southern Indian state of Tamil Nadu killed 18 hospital patients this week after rainwaters knocked out generators and switched off ventilators, officials said Saturday.

State authorities were investigating complaints of negligence by officials at MIOT International hospital in the state capital of Chennai, which is reeling from massive floods.

The 18 patients were in the intensive care unit when a power outage affected ventilators in the hospital, leading to their deaths over the past two to three days, said state Health Secretary J. Radhakrishnan.

He said that floodwaters entered the room with the generators, cutting off power to the building and switching off the ventilators.

More than 280 people have died due to the floods in Chennai, a city of 9.6 million, and nearby districts, including several who were killed due to electric shocks from power distribution boxes that had been submerged by floodwaters. Authorities have turned off power supplies in some areas to prevent accidental deaths.

Army soldiers using boats have rescued thousands of residents marooned in high-rise buildings and launched massive relief operations to provide food and medicine.

Although floodwaters have begun to recede, vast swaths of Chennai and neighboring districts were still under 2 1/2 to 3 meters (8 to 10 feet) of water, with tens of thousands of people in state-run relief camps.

As officials struggled to supply drinking water and food packets, people were complaining that relief had not yet reached several neighborhoods, four days after they were marooned or stranded on rooftops. With no electricity for more than four days, they had no way to charge their cellphones, they said.

“We feel quite helpless,” said Malti Soman, standing in knee-deep water in Mambalam, a residential area in central Chennai. “The landline phones are not working. And my cellphone is dead because there is no electricity to charge it.”

Radhakrishnan, the health secretary, said Saturday that while the immediate rescue operations were tapering off, the main focus of the administration in the coming days will be to prevent the spread of communicable diseases.

In many areas, sewage drains have overflowed due to the rising floodwaters, posing a health hazard for residents who have had to wade through the water, Radhakrishnan said.

“This is a concern,” he said. “We are working with the local water and sewage agencies to disinfect the worst-hit areas.”

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