Flooding across the northwestern state killed at least 29 people and affected over 250,000 last month, with the state's chief minister calling it "one of the worst flood disasters in decades".

The region is often dubbed India's breadbasket, but more than 940 square kilometres (360 square miles) of farmland are flooded, leading to "devastating crop losses", Punjab's Chief Minister Bhagwant Mann wrote in a letter to Prime Minister Narendra Modi.

Modi on Monday assured him of the federal government's "full support".

Authorities have said they fear a "huge loss of livestock", the full extent of which will only be clear when the waters recede, according to a bulletin issued by the state authorities late Monday.

India's army and disaster teams have carried out vast rescue operations, deploying more than 1,000 boats and 30 helicopters to rescue the stranded or supply food.

"The most important thing is to save the lives of people and helpless animals trapped in the water," Mann said in a statement.

Rivers in the region cross into Pakistan, where floodwater has also engulfed swathes of land.

Floods and landslides are common during the June-September monsoon season in the subcontinent, but experts say climate change, coupled with poorly planned development, is increasing their frequency, severity and impact.

Northwest India has seen rainfall surge by more than a third on average from June to September, according to the national weather department.

In the capital Delhi, relentless rains have swollen the Yamuna river -- which breached its danger mark on Tuesday, inundating several areas and creating traffic snarl-ups lasting for hours.

Deadly floods triggered by record-breaking rain also killed dozens in India's Jammu and Kashmir region last month.