Elon Musk tweeted Friday that Tesla and SpaceX employees are “working on ventilators” even though he doesn’t believe they will be needed.

His confirmation on Twitter that both of the companies he leads are working on ventilators comes a day after New York City Mayor Bill de Blasio made a direct plea to Musk to help alleviate a shortage at hospitals gearing up to combat COVID-19.

Yes, we’re working on ventilators, even though I think they probably won’t be needed — Elon Musk (@elonmusk) March 20, 2020

It’s unclear how many employees are working on the ventilators and which Tesla factory — it could be Buffalo, N.Y., Fremont, Calif., Sparks, Nev. or even Shanghai — has dedicated space to the project. The SpaceX facility is located in Hawthorne, Calif.

Musk didn’t describe what capacity would be or how long it might take to scale up such an endeavor. One Twitter follower recommended building one large ventilator with multiple branches and lines. Musk noted that a single computer, pump and pressure accumulator could do the job, but noted that individual valves per patient would be ideal.

Whatever Musk decides, his project still faces specific obstacles. Certified medical personnel will need to be involved in such an operation and ventilator hardware used in clinical settings still must be approved by the FDA, which could delay production.

A single computer, pump & pressure accumulator would be fine for many patients, but ideally individual valves per patient to personalize care & avoid cross-flow risk — Elon Musk (@elonmusk) March 20, 2020

Still, the need for ventilators is urgent, prompting other automakers to investigate ways of ramping up production. GM, Volkswagen and Ford have all reportedly either talked to the White House or committed to looking at the problem. Volkswagen said Friday it has created a task force to look into using 3D printing to make hospital ventilators.

De Blasio tweeted out his plea to Musk Thursday morning. “Our country is facing a drastic shortage and we need ventilators ASAP — we will need thousands in this city over the next few weeks. We’re getting them as fast as we can but we could use your help!”

The mayor’s office has reached out to the person who runs Musk’s family office, his communications director and his lobbyist, press secretary Freddi Goldstein told TechCrunch in an email. “Given his response on Twitter, we’re hopeful he will be able to help,” Goldstein added

The COVID-19 pandemic had elicited a seemingly conflicting mix of responses from Musk. He has downplayed COVID-19 in emails to employees and on social media. In one company-wide email sent to SpaceX employees, Musk wrote that they have a higher risk of being killed in a car crash than dying from the coronavirus, BuzzFeed reported last week.

Since then, Musk wrestled with officials in Alameda County to keep Tesla’s Fremont, Calif., factory open, in spite of a government directive to close all non-essential businesses. Tesla announced plans Thursday to suspend production there beginning March 23.

Some basic operations that would support Tesla’s charging infrastructure and what it describes as its “vehicle and energy services operations” will continue at the factory, which under normal circumstances employs more than 10,000 people. Tesla is also suspending operations at its factory in Buffalo, N.Y., except for “those parts and supplies necessary for service, infrastructure and critical supply chains,” the company said in a statement.

Musk has jumped into crises before with mixed results. In 2018, Musk and the Musk Foundation donated $480,350 to add ultraviolet water filtration systems and water stations to all 12 area schools in Flint, Mich. The effort was delayed but eventually the systems were installed, beginning in fall 2019.

In 2018, he put SpaceX engineers to work on a pod that could be used to save children trapped in a flooded cave in Thailand. Rescuers didn’t use the device and an argument with a cave diving expert that played out on social media and national television led to a defamation lawsuit, after Musk repeatedly called him “pedo guy.” Musk was found not liable for defamation in a federal court in 2019.