MUMBAI (Reuters) - India's June-September monsoon has started withdrawing from the north-western region, the weather department said on Thursday, which could increase the rainfall deficit for the season.

The monsoon usually starts withdrawing in the first week of September.

"The southwest monsoon has withdrawn from some parts of West Rajasthan today," the weather department said.

The July-September rains irrigate nearly half of India's farmlands, bringing relief to millions of poor farmers who till small plots of land to sustain their families.

The country has so far received 5 percent lower rainfall than normal in the current monsoon season.

Monsoon rains in India, the world's second-biggest producer of rice and sugar, could be lighter than average this year in the absence of the La Nina weather pattern, two senior officials at the state-run weather department said.

(Reporting by Rajendra Jadhav; Editing by Sunil Nair)