The Deniliquin mill, the largest rice mill in the Southern Hemisphere, once processed enough grain to meet the needs of 20 million people around the world. But six long years of drought have taken a toll, reducing Australia’s rice crop by 98 percent and leading to the mothballing of the mill last December.

Ten thousand miles separate the mill’s hushed rows of oversized silos and sheds — beige, gray and now empty — from the riotous streets of Port-au-Prince, Haiti, but a widening global crisis unites them.

The collapse of Australia’s rice production is one of several factors contributing to a doubling of rice prices in the last three months — increases that have led the world’s largest exporters to restrict exports severely, spurred panicked hoarding in Hong Kong and the Philippines, and set off violent protests in countries including Cameroon, Egypt, Ethiopia, Haiti, Indonesia, Italy, Ivory Coast, Mauritania, the Philippines, Thailand, Uzbekistan and Yemen.