SAN FRANCISCO, United States (AFP) — Employee departures were multiplying at Twitter after an ultimatum from new owner Elon Musk, who demanded staff choose between being "extremely hardcore" and working intense, long hours, or losing their jobs.

"I may be #exceptional, but gosh darn it, I'm just not #hardcore," tweeted one former employee, Andrea Horst, whose LinkedIn profile still reads "Supply Chain & Capacity Management (Survivor) @Twitter."

She added the hashtag "#lovewhereyouworked," as did many other employees announcing their choice.

Musk, also the CEO of Tesla and SpaceX, has come under fire for radical changes at the social media company, which he bought for $44 billion late last month.

He had already fired half of the company's 7,500 staff, scrapped a work-from-home policy and imposed long hours, all while his attempts to overhaul Twitter have faced chaos and delays.

"Going forward, to build a breakthrough Twitter 2.0 and succeed in an increasingly competitive world, we will need to be extremely hardcore," Musk wrote in the ultimatum, an internal memo sent Wednesday and seen by AFP.