A TINY toxic mushroom was believed to be behind hundreds of deaths in southwestern China.

According to medical investigators, the relatively unknown Little White fungus caused the fatalities, Sky News reported.

At least 400 people mysteriously died from cardiac arrest over the last 30 years, in what is known as Yunnan Sudden Death Syndrome.

In 2004, local health officials appealed to Beijing for help in finding the killer and a team of medical investigators from The Chinese Centre for Disease Control and Prevention (CDC) were handling the inquiry.

Investigators focused on mushrooms because while deaths were spread out in different villages in the Yunnan province, more than 90 percent occurred mainly in the mushroom harvesting season during July and August.

By 2008, investigators discovered the Little White, from the Trogia species, in a number of homes where people had died.

Robert Fontaine, a US epidemiologist who took part in the investigation, said: "What we have here is a toxin that is picking off vulnerable people."

Read more about toxic mushroom being blamed for 400 China deaths at Sky News.

