The U.S. Department of Health and Human Services (HHS) on Tuesday began its mass layoffs, dismissing thousands of employees across various agencies, U.S. media reported.

Significant budget cuts to divisions of the HHS, such as the Food and Drug Administration, the Centers for Disease Control and Prevention, and the National Institutes of Health, among others, have raised serious concerns about public health and scientific research.

"The Trump administration laid off thousands of federal health workers on Tuesday in a purge that included senior leaders and top scientists charged with regulating food and drugs, protecting Americans from disease and researching new treatments and cures," The New York Times reported.

The report quoted workers as saying that layoff notices began arriving at 5:00 a.m. local time (1000 GMT), affecting offices responsible for everything from global health to food safety.

Staff had to present their badges at the building entrance and those who had been fired were given a ticket and "told to return home," USA Today reported.

"Infectious disease experts, including those addressing HIV, argued the latest HHS cuts will make the country less safe from infectious and chronic diseases," the report said.

"The FDA as we've known it is finished, with most of the leaders with institutional knowledge and a deep understanding of product development and safety no longer employed," wrote Robert Califf, former two-term commissioner at the Food and Drug Administration, in a post on LinkedIn.

"I believe that history will see this a huge mistake," said Califf.

The HHS announced Thursday its plan to cut about 10,000 full-time employees as part of its "restructuring" effort.

Including early retirements and the government's buyout program, the department's full-time workforce will be reduced from 82,000 to 62,000.