Amazon CEO Jeff Bezos sent a memo to employees Saturday addressing concerns about warehouse worker safety amid the coronavirus outbreak.

In the memo, posted to Amazon's website, Bezos writes, "There is no instruction manual for how to feel at a time like this, and I know this causes stress for everyone." He also acknowledged that "much of the essential work we do cannot be done from home," but that Amazon has taken a number of steps to improve safety at its facilities and is "working to identify additional ways to improve on these measures."

Bezos told his employees in the memo that the company has placed purchase orders for millions of face masks for workers who can't do their job remotely, but "very few of those orders have been filled" as masks remain in short supply. "When our turn for masks comes, our first priority will be getting them in the hands of our employees and partners working to get essential products to people," he added.

Workers and legislators have criticized Amazon for requiring fulfillment center employees and delivery drivers to come to work as the coronavirus has continued to spread. Unlike employees at Amazon's corporate offices, which have been told to work remotely, warehouse workers and delivery drivers cannot carry out their job duties while working from home.

At the same time, many workers have raised concerns that they risk getting sick on the job. Amazon on Thursday temporarily closed a Queens, New York delivery station, known as DBK1, after a worker tested positive for the COVID-19 coronavirus. The case marked the first known incident of a U.S. Amazon warehouse employee contracting the disease. On Monday, Amazon confirmed that at least five workers at Amazon warehouses in Spain and Italy contracted the disease.

Earlier this month, Amazon logistics workers circulated a petition calling for the company to put in place more "protective measures," including giving workers paid leave, to "ensure the safety of all of its workers and the larger public."

On Friday, four senators sent a letter to Amazon urging the company to better protect warehouse workers during the coronavirus outbreak. The senators urged Bezos to provide paid sick leave and time-and-a-half hazard pay for its workers, among other measures.

Amazon previously told CNBC it implemented "proactive measures" to protect fulfillment center employees, including increased cleaning at all facilities and maintaining social distance by suspending team meetings at the beginning of shifts, halting exit screening and staggering shift start times and break times, among other measures.

Amazon said Saturday it's doubling hourly wages for its associates working overtime in its U.S. warehouses. The temporarily increased overtime pay continues through May 9.

The company also recently announced it would provide up to two weeks of pay to all employees diagnosed with the coronavirus or placed into quarantine, as well as provide unlimited unpaid time off for all hourly employees through the month of March.

Here's the full memo:

Dear Amazonians,

This isn't business as usual, and it's a time of great stress and uncertainty. It's also a moment in time when the work we're doing is its most critical.

We've changed our logistics, transportation, supply chain, purchasing, and third party seller processes to prioritize stocking and delivering essential items like household staples, sanitizers, baby formula, and medical supplies. We're providing a vital service to people everywhere, especially to those, like the elderly, who are most vulnerable. People are depending on us.

I'm not alone in being grateful for the work you are doing. I've received hundreds of emails from customers and seen posts on social media thanking you all. Your efforts are being noticed at the highest levels of government, and President Trump earlier this week thanked this team profusely.

Across the world, people are feeling the economic effects of this crisis, and I'm sad to tell you I predict things are going to get worse before they get better. We're hiring for 100,000 new roles and raising wages for our hourly workers who are fulfilling orders and delivering to customers during this period of stress and turmoil. At the same time, other businesses like restaurants and bars are being forced to shut their doors. We hope people who've been laid off will come work with us until they're able to go back to the jobs they had.

Much of the essential work we do cannot be done from home. We've implemented a series of preventative health measures for employees and contractors at our sites around the world — everything from increasing the frequency and intensity of cleaning to adjusting our practices in fulfillment centers to ensure the recommended social distancing guidelines. We are meeting every day, working to identify additional ways to improve on these measures.

We've placed purchase orders for millions of face masks we want to give to our employees and contractors who cannot work from home, but very few of those orders have been filled. Masks remain in short supply globally and are at this point being directed by governments to the highest-need facilities like hospitals and clinics. It's easy to understand why the incredible medical providers serving our communities need to be first in line. When our turn for masks comes, our first priority will be getting them in the hands of our employees and partners working to get essential products to people.

My own time and thinking is now wholly focused on COVID-19 and on how Amazon can best play its role. I want you to know Amazon will continue to do its part, and we won't stop looking for new opportunities to help.

There is no instruction manual for how to feel at a time like this, and I know this causes stress for everyone. My list of worries right now — like yours I'm sure — is long: from my own children, parents, family, friends, to the safety of you, my colleagues, to those who are already very sick, and to the real harm that will be caused by the economic fallout across our communities.

Please take care of yourselves and your loved ones. I know that we're going to get through this, together.

Jeff