Diabetes is expected to affect nearly 400 million people, about seven per cent of the world's adult population, by 2025, a conference heard Monday.

"The biggest challenge of today is to communicate the magnitude of the epidemic throughout the world," Pierre Lefebvre, outgoing president of the International Diabetes Federation, told delegates on the first day of a four-day meeting in Cape Town on Monday.

New data suggest the number of people living with diabetes will skyrocket to 380 million within 20 years if nothing is done, the federation said in its new diabetes atlas.

Diabetes kills 3.8 million people a year — as many people as HIV/AIDS, according to the atlas.

"Diabetes is fast becoming the epidemic of the 21st century," the report said.

The condition occurs when the body cannot produce or use insulin properly to process sugar. It already affects 246 million people worldwide, up from 30 million two decades ago.

More children and teens are being affected by Type 2 diabetes.

"There is no doubt that this is linked to the epidemics of overweight and obesity, and there is no doubt that this increase in overweight and obesity is linked to the profound way in which the life of those children and adolescents has changed over the past 10 to 20 years," Pierre Lefebvre, the group's outgoing president, told delegates.

India and China have the highest number of diabetics at around 40 million each, the report said. Type 2 diabetes is spreading the fastest in the Eastern Mediterranean and Middle East.

"Wherever poverty and a lack of sanitation drive families to low cost-per-calorie foods and packaged drinks, Type 2 diabetes thrives," the federation said in a statement.

Overweight and obesity are risk factors for Type 2 diabetes. Type 1 diabetes has no known cause and makes up a minority of cases.