Roads are damaged, mobile phone networks are down, an international airport has been closed and more than 220,000 people have been left homeless after unusually heavy rain in the past nine days.

Officials repeatedly revised the death toll upwards from 86 people on Friday morning to more than 300 by the evening as a massive rescue operation reached more flood-hit regions. “Around 100 people died in the last 36 hours alone,” a state official said.

Casualty numbers are expected to increase further, with thousands more people still stranded and less intense though still heavy rain forecast for at least the next 24 hours. Many have died from being buried in hundreds of landslides set off by flooding.

The toll in Kerala contributed to more than 900 deaths recorded by the Indian home ministry this monsoon season from landslides, flooding and rain.

Rescue workers and members of India’s armed forces have been deployed across the state with fleets of ships and aircraft brought in to save the thousands of people still stranded, many sheltering on their roofs signalling to helicopters for help.

Meteorologists said Kerala had received an average 37.5% more rainfall than usual. The hardest-hit districts such as Idukki in the north received 83.5% excess rain. More than 80 dams across the state had opened their gates to try to ease the crisis, the chief minister said.