The White House says it will redirect $US589 million ($A781.5 million) in funds to prepare for and respond to the Zika virus before the mosquito that carries it begins to emerge in the continental United States.
But White House budget director Shaun Donovan said the move was only a temporary fix for Zika funding, adding that some measures would have to be delayed, curtailed or stopped unless the US Congress approves an emergency funding request for more than $US1.8 billion, made earlier this year.
The virus, linked to numerous cases of the birth defect microcephaly in Brazil, is spreading rapidly in Latin America and the Caribbean and heading north as the weather gets warmer.
Health and Human Services Secretary Sylvia Mathews Burwell said that without the requested emergency funding, the US risked its ability to respond to the virus.
Burwell said mosquito control and surveillance may have to be delayed or stopped, vaccine development could be jeopardised and development of faster diagnostic tests could be impaired.
"We should not play with fire here," Donovan told reporters on a conference call on Wednesday.
The Republican-controlled Congress has said the White House should draw the money it needs to fight Zika from $US2.7 billion in funds set aside for public health projects aimed at the Ebola virus.
Burwell said the White House still needs the full emergency funding and cannot risk short-changing efforts to help West African countries fight Ebola.
"We face two global health challenges, Ebola and Zika, and we don't have an option to set one aside in the name of the other," Burwell told reporters.
Burwell said there were already 672 confirmed cases of Zika infections in the continental United States and US territories, including in 64 pregnant women.
She said there was one confirmed case of Zika-related microcephaly in Hawaii.
