Washington: US House Speaker Nancy Pelosi has slammed Donald Trump for his administration's "opaque and often chaotic" response to the coronavirus as stock markets tumbled.

The US Centre for Diseases and Control Prevention on Thursday (AEDT) confirmed what appears to be first American case of a "community spread" of the virus in California, adding to the 60 confirmed US cases of illness caused by COVID-19.

A day after the US President labelled her "incompetent" and accused her of trying to create panic, Pelosi told reporters in Washington: "Lives are at stake - this is not a time for name-calling or playing politics.

"The first step the Congress must take is to ensure that the government has the resources it needs to combat this deadly virus and keep Americans safe... Unfortunately, up until now, the Trump administration has mounted an opaque and often chaotic response to this outbreak."