Dr Rachel Levine, the United States assistant health secretary, was sworn in as the country's first transgender four-star officer on Tuesday, local media reported.

The 63-year-old was picked by US President Joe Biden to be his assistant secretary of health in January and her appointment was confirmed by the Senate earlier this year. She is also the highest-ranking openly transgender official in the US.

Levine is now an admiral of the US Public Health Service Commissioned Corps — a 6,000-strong force that responds to health crises, including administering coronavirus vaccines and providing medical aid after natural disasters, according to a report by The Washington Post.

During her swearing-in ceremony, Levine described it as a "momentous" and "historic" occasion, the British Broadcasting Corporation (BBC) reported.

"May this appointment today be the first of many more to come, as we create a diverse and more inclusive future," the report quoted her as saying.

Separately, in an interview, Levine emphasised that her position as an admiral was "not just symbolic" and she would take a leading role in shaping the public health corps' priorities, The Washington Post report stated.

She added that she would start wearing the uniform of the US Public Health Service Commissioned Corps immediately.

Prior to her appointment as assistant health secretary, Levine had been serving as the US state of Pennsylvania's top health official since 2017 and emerged as the public face of the state's response to the coronavirus pandemic.

A graduate of Harvard and of Tulane Medical School, Levine is president of the Association of State and Territorial Health Officials. She has written in the past on the opioid crisis, medical marijuana, adolescent medicine, eating disorders and LGBTQ (lesbian, gay, bisexual, transgender and queer) medicine.