(Reuters) - Tesla (NASDAQ: ) Inc's Chief Executive Officer Elon Musk tweeted on Friday that the coronavirus "panic" was "dumb".

The number of people infected with coronavirus surpassed 100,000 across the world on Friday. The outbreak has killed more than 3,400 people and spread across more than 90 nations, with six countries reporting their first cases.

Stock markets have plunged and concerns have led to shortages of face masks, disinfectant and other items. Companies across the world are changing the way they work, asking and requiring employees to work from home, for instance, and stopping corporate travel.

Tesla stock is down more than 20% since the news of the virus outbreak triggered a broader sell-off in the stock market around mid February.

Billionaire Musk, with more than 30 million followers, has a history of being outspoken on his Twitter account, one of corporate America's most-watched.