The U.S. tally of monkeypox cases crossed 6,600 on Wednesday, almost all of them among men who have sex with men.
"We're prepared to take our response to the next level in addressing this virus, and we urge every American to take monkeypox seriously," Health and Human Services Secretary Xavier Becerra said at a briefing.
The declaration will also help improve the availability of monkeypox data, U.S. Centers for Disease Control and Prevention Director Rochelle Walensky said, speaking alongside Becerra.
The World Health Organization also has designated monkeypox a "public health emergency of international concern," its highest alert level. The WHO declaration last month was designed to trigger a coordinated international response and could unlock funding to collaborate on vaccines and treatments.
Biden earlier this month appointed two top federal officials to coordinate his administration's response to monkeypox, following declarations of emergencies by California, Illinois and New York.
First identified in monkeys in 1958, the disease has mild symptoms including fever, aches and pus-filled skin lesions, and people tend to recover from it within two to four weeks, according to the WHO. It spreads through close physical contact and is rarely fatal.
Anthony Fauci, Biden's chief medical adviser, told Reuters on Thursday that it was critical to engage leaders from the gay community as part of efforts to rein in the outbreak, but cautioned against stigmatizing the disease and its victims.
"Engagement of the community has always proven to be successful," Fauci said.
Unlike when COVID-19 emerged, there are vaccines and treatments available for monkeypox, which was first documented in Africa in the 1970s.
The U.S. government had distributed 156,000 monkeypox vaccine doses nationwide through mid-July. It has ordered an additional 2.5 million doses of Bavarian Nordic's vaccine.
The first U.S. case of monkeypox was confirmed in Massachusetts in May, followed by another case in California five days later.