India on Monday banned the exports of onion as prices continued to surge in a month after excessive rainfall hit crops in southern states. The government said the export of all varieties of onion has been prohibited with the immediate effect. Wholesale prices in India's largest onion trading hub, Lasalgaon in the western state of Maharashtra, have nearly trebled in a month to 30,000 rupees per tonne. India is the world's biggest exporter of onions, a staple of South Asian cooking. Countries such as Bangladesh, Nepal, Malaysia and Sri Lanka rely on Indian shipments.