The US Centers for Disease Control and Prevention has alerted Americans to begin preparing for the spread of coronavirus in the United States after infections surfaced in several more countries.

The announcement signalled a change in tone for the Atlanta-based US health agency, which had largely been focused on efforts to stop the virus from entering the country and quarantining individuals travelling from China.

"The data over the past week about the spread in other countries has raised our level of concern and expectation that we are going to have community spread here," Doctor Nancy Messonnier, the CDC's head of respiratory diseases, told reporters on a conference call.

What is not known, she said, is when it will arrive and how severe a US outbreak might be. "Disruption to everyday life might be severe" and businesses, schools and families should begin having discussions about the possible impact from the spread of the virus, Messonnier cautioned.

In a teleconference later on Tuesday, Doctor Anne Schuchat, the CDC's principal deputy director, said that while the immediate risk in the United States was low, the current global situation suggested a pandemic was likely.

"It's not a question of if. It's a question of when and how many people will be infected," Schuchat said.

Separately, US Health and Human Services Secretary Alex Azar told a Senate subcommittee there will likely be more cases in the United States, and he asked lawmakers to approve $US2.5 billion ($A3.8 billion) in funding to fight the outbreak after proposing cuts to the department's budget.

Believed to have originated from illegal wildlife sold in the Chinese city of Wuhan late last year, the new coronavirus has infected some 80,000 people and killed close to 2700 in China.

Although the World Health Organisation says the epidemic has peaked in China, coronavirus cases have surfaced in about 30 other countries, with some three dozen deaths reported, according to a Reuters tally.

Growing outbreaks in Iran, Italy and South Korea have raised concerns that coronavirus will surface in other nations and worsen in those that have already reported infections, further denting a global economy that had already been hit by a dependence on China.

Global and US stock markets fell sharply again on Tuesday, as investors feared the epidemic would further damage an already slowing world economy.

© RAW 2020