The US will declare a public health emergency to bolster the federal response to the monkeypox outbreak that has infected more than 6600 Americans, two people familiar with the matter said Thursday.

The announcement will free up federal money and other resources to fight the virus, which may cause fever, body aches, chills, fatigue and pimple-like bumps on many parts of the body. The people spoke on the condition of anonymity ahead of an official announcement.

The declaration comes as the Biden administration has faced criticism over monkeypox vaccine availability. Clinics in major cities such as New York and San Francisco say they haven't received enough of the two-shot vaccine to meet demand, and some have had to stop offering the second dose to ensure supply of first doses.

The White House said it has made more than 1.1 million doses available and has helped to boost domestic diagnostic capacity to 80,000 tests per week.

The monkeypox virus spreads through prolonged and close skin-to-skin contact, including hugging, cuddling and kissing, as well as sharing bedding, towels and clothing. People who have become sick so far have been primarily men who have sex with men. But health officials emphasise that the virus can infect anyone.

The announcement comes three days after the Biden administration named top officials from the Federal Emergency Management Agency and the Centers for Disease Control and Prevention to serve as the White House coordinators to combat the monkeypox outbreak.

News of the expected declaration was first reported Thursday by Politico.

Such a declaration is an important — and overdue — step, said Lawrence Gostin, a public health law expert at Georgetown University.

"It signals the US government's seriousness and purpose, and sounds a global alarm."

Under a declaration by the Department of Health and Human Services, the agency can draw from emergency funds, hire or reassign staff to deal with the outbreak, and take other steps to control the virus.

Daniel Rofin, 41, receives a vaccine against Monkeypox from a health professional in medical center in Barcelona, Photo / AP

A public health emergency can be extended, similar to what happened during the Covid-19 pandemic.

Gostin said the US government has been too cautious and should have declared a nationwide emergency earlier. Public health measures to control outbreaks have increasingly faced legal challenges in recent years, but Gostin didn't expect that to happen with monkeypox.

"It is a textbook case of a public health emergency," Gostin said. "It's not a red or a blue state issue. There is no political opposition to fighting monkeypox."

The government's decision comes after others have made similar declarations.

Last week, the World Health Organisation called monkeypox a public health emergency, with cases in more than 70 countries. A global emergency is the WHO's highest level of alert, but the designation does not necessarily mean a disease is particularly transmissible or lethal.

California, Illinois and New York have all made declarations in the last week, as have New York City, San Francisco and San Diego County.

- AP