Short sellers have focused their attention on Warren Buffett's Berkshire Hathaway, with the number of the firm's B shares on loan increasing fivefold, as hedge funds look to profit from concerns over the industrial conglomerate's multi-billion dollar takeover of a US railway operator.

Berkshire Hathaway announced a $36bn (€24bn) deal to acquire the remaining 77.4% of US railway operator Burlington Northern Santa Fe Corporation that it does not already own on November 3.