Bill Gates has warned a biological terror attack more destructive than a nuclear attack could wipe out 30 million people.

The Microsoft founder warned that terrorists could recreate diseases such as smallpox to wreak havoc in the heart of the West.

Speaking ahead of a speech at the Royal United Services Institute in London, the billionaire said: “Bioterrorism is a much larger risk than a pandemic.

“All these advances in biology have made it far easier for a terrorist to recreate smallpox, which is a highly fatal pathogen, where there is essentially no immunity remaining at this point.

“When you are thinking about things that could cause in excess of 10 million deaths, even something tragic like a nuclear weapons incident wouldn’t get to that level. So, the greatest risk is from a natural epidemic or an intentionally caused infection bioterrorism events.”

He said a “fast-moving airborne” disease could kill 30 million people in less than a year.

Gates added: “Whether the next epidemic is unleashed by a quirk of nature or the hand of terrorist, scientists say a fast-moving airborne pathogen could kill more than 30 million people in less than a year.

“So the world does need to think about this.”

This is not the first time Mr. Gates has claimed bioterrorism could claim the lives of more people than nuclear terror attacks.

Earlier this year, he said: “With nuclear weapons, you’d think you would probably stop after killing 100 million.”