At least eight people have died and a dozen are feared missing after a day of torrential rain in the southern Indian state of Kerala.

Rescue operations are continuing on Sunday after downpours lashed the state the day before, triggering flash floods and landslides.

The National Disaster Response Force and the Indian Army have deployed teams to help with rescue efforts in two of the worst-hit districts, Kottayam and Idukki, where a dozen people are still feared missing.

Rain clouds
Dark rain clouds gathered over Kochi, Kerala state, before the downpours began on Saturday (R S Iyer/AP)

On Saturday, when the heavy rain began, television reports showed people wading through chest-deep waters to rescue passengers from a bus that was nearly submerged by the torrents flooding the roads.

Officials said the intense rainfall has subsided, but they fear the death toll could rise as relief and rescue operations continue.

Home minister Amit Shah said the federal government is monitoring the situation in Kerala and will provide all possible support to the state.

In 2018, Kerala suffered catastrophic floods when heavy downpours amid the monsoon season killed 223 people and drove hundreds of thousands from their homes.