Twitter CEO Jack Dorsey’s official account has been hacked, sending racist and vulgar tweets to his 4.2 million followers.

The person tweeting from Mr Dorsey’s account on Friday sent tweets such as “Hitler is innocent” and, using a vulgarity, asked “bald skeleton head”, referring to the Twitter chief, to un-suspend his account.

Twitter says it is investigating.

The tweets were up for about 30 minutes before Twitter took them down.

The company also suspended accounts that the hacker or hackers retweeted while they had control of Mr Dorsey’s account.

The incident comes as Twitter and Mr Dorsey have promised to improve the “health” and civility of discourse on the social media service, cracking down on hate speech and abuse.