The top U.S. infectious disease expert Anthony Fauci on Tuesday warned Congress that the development of a vaccine against COVID-19 "might take some time" even though the federal government is working to help in its manufacture.

In his address to the Senate health committee, Fauci said the country's efforts against the disease should be "focused on the proven public health practices of containment and mitigation."

The infectious disease expert had earlier warned against rushing to ease restrictions aimed at curbing the spread of COVID-19, saying that would put lives at risk and hamper economic recovery.

Fauci was set to appear on Tuesday at the Republican-controlled Senate committee on health, education, labor and pensions after the White House blocked the 79-year-old infectious disease expert from testifying to a Democratic-controlled House of Representatives panel, calling it "counterproductive."

His appearance came as some of the U.S. states rolled out reopening plans as the country took a battering from the effects of the pandemic.

The White House is also keen on reopening the country. In the latest move geared towards the same, President Donald Trump on Tuesday urged California to allow "Tesla and Elon Musk open the plant, NOW."

Other people who were lined up to testify on Tuesday include U.S. Centers for Disease Control and Prevention Director Robert Redfield, Assistant Secretary for Health Brett Giroir and Food and Drug Administration Commissioner Stephen Hahn.