Twitter has said it is investigating after CEO Jack Dorsey has had his account hacked with a series of racist tweets posted online.

The flurry of offensive messages were posted to Mr Dorsey’s 4.2 million followers this evening.

A spokesperson for Twitter said: "We're aware that Jack was compromised and are investigating what happened."

The offensive tweets - which included false reports of a bomb threat at Twitter HQ - were quickly deleted.

The account also re-tweeted posts from several individuals claiming to be responsible.