Eighteen patients died in a hospital in Chennai after rainwaters knocked out the building’s generators and power to their ventilators, officials have said, as the state of Tamil Nadu in southern India reels from a week of severe flooding.

State officials are investigating complaints of negligence on the part of hospital authorities in the state capital Chennai, which is suffering from unprecedented floods.

The state’s health secretary, J. Radhakrishnan, said 18 patients were in the intensive care unit when a power outage affected ventilators in the hospital.

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

Tens of thousands of people are still in relief camps Saturday as they wait for the floods to recede.