The head of the U.S. Federal Reserve warned of an "extended period" of weak economic growth sparked by the novel coronavirus pandemic.

In a webcast interview with the Peterson Institute for International Economics(PIIE) on Wednesday, Fed Chair Jerome Powell warned of the threat of a serious downturn, which could lead to protracted low productivity growth and stagnant incomes.

Assessing that the U.S. response to date "has been particularly swift and forceful," Powell, however, said the longer health risks persist, the more likely businesses will fail and households will be strapped for income.

Citing uncertainty over how well future outbreaks can be controlled and how quickly a vaccine or therapy can be developed, he called for additional fiscal spending to stem the fallout from the pandemic.

Powell vowed to fully utilize the Fed's tools in overcoming the crisis, but dismissed the idea of pushing interests rates below zero, saying it is not a measure being considered.