Rob Arnott, founder and chair of US-based Research Affiliates, warns several of the world's biggest technology stocks are "in clear bubble" territory, claiming they have “implausible growth assumptions”.

Arnott said Facebook, Amazon, Netflix, Microsoft, Apple and Google — dubbed Fanmag — represent an aggregate market capitalization of more than $8tn. That's more than the publicly-traded portion of the Japanese economy and nearly as much as all of China.