San Francisco,  Elon Musk's Twitter is reeling under a big trouble as another 1,200 employees have quit over the ultimatum for "extremely hardcore" workplace.

The New York Times reported that key infrastructure teams have been "decimated" at Twitter and Musk sent an email to employees asking them about the details regarding the underlaying technology.

"Anyone who actually writes software, please report to the 10th floor at 2 p.m. today," Musk said in the email on Friday.

"Before doing so, please email me a bullet point summary of what your code commits have achieved in the past 6 months, along with up to 10 screenshots of the most salient lines of code," he posted.

Musk earlier sacked 50 per cent of the Twitter workforce, as several key executives resigned.

After hundreds of employees resigned from the company ahead of the deadline, Musk said that he is not "super" worried about the mass resignations as the best employees are staying.

Several employees took to Twitter to announce their resignations ahead of the deadline to meet Musk's new work criteria.