Twitter CEO Jack Dorsey has found his official account hacked and sending racist and vulgar tweets to his 4.2 million followers.

The person tweeting from Dorsey's account on Friday sent tweets such as "Hitler is innocent" and, using a vulgarity, asked "bald skeleton head," referring to Dorsey, to unsuspend his account.

Twitter says it's 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 Dorsey's account.

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

"We're aware that @jack was compromised and investigating what happened," a Twitter spokesperson said.

Some of the tweets contained the hashtag #ChucklingSquad which was believed to indicate the identity of the hacker group.

The news comes with Dorsey and Twitter moving aggressively to clean up offensive and inappropriate content as part of a focus on "safety."