The annual monsoon, crucial to India's food output and economic growth, hit the southwest coast on Saturday, bringing cheer to farmers and boosting hopes for the struggling economy.

The keenly awaited rains lashed the state of Kerala and parts of neighbouring Tamil Nadu and will now sweep across India, resulting in torrential downpours over the coming months for hundreds of millions of farmers who rely on the seasonal precipitation.

"The southwest monsoon has set in over Kerala," the weather office announced on its website.

The rains that lash the subcontinent from June to September are dubbed the "economic lifeline" of India, one of the world's leading producers of rice, sugar, wheat and cotton.

The rains normally hit the southwest coast at the start of June but memories remain fresh of India's devastating drought in 2009 that resulted in shrivelled crops.

The weather department has forecast India will receive normal rains this year, raising prospects of a stronger performance by Asia's third-largest economy.

India's 235 million farmers still rely on the erratic rains to soak around 60 percent of the country's farmland -- despite calls for the government to improve irrigation and water-harvesting methods to ensure more stable crop output.

The rains are crucial this year for central parts of the western state of Maharashtra, India's biggest sugar-producer, which has been reeling from the worst drought in over four decades.

Last year India got below-normal rain in the first half of the wet season. The rains picked up in some areas later, but large areas of west and south India did not benefit.

The Congress-led national government's hopes of at least six percent economic growth this financial year -- up from a decade low of five percent last year -- hinge on a normal monsoon.

A good monsoon is also vital for the ruling Congress party ahead of elections due in 2014 as it struggles to kickstart growth in the country of 1.2 billion people.

Agriculture contributes about 15 percent to gross domestic product but the livelihood of hundreds of millions of Indians living in rural areas depends on the farming sector.