The US state of Ohio likely has more than 100,000 people carrying the new coronavirus, the state health department director said.

Speaking at a press conference Thursday with state governor Mike DeWine to announce measures to slow the spread of the pandemic, director Amy Acton said Ohio had community spread of the virus.

"We know now just the fact of community spread says that at least one percent, at the very least, one percent of our population is carrying this virus in Ohio today," Acton said.

"We have 11.7 million people. So the math is over 100,000. So that just gives you a sense of how this virus spreads and is spreading quickly," she said.

"It is this one-in-50 years pandemic that we've been planning for."

Ohio has five confirmed cases and 52 under investigation but, like much of the United States, has so far carried out limited numbers of tests.

Coronavirus cases in the United States surpassed 1,300 on Thursday with nearly 40 deaths, according to data from Johns Hopkins University.

As of Sunday, 1,707 Americans had been tested, Business Insider reported, citing data from the Centers for Disease Control and Prevention (CDC). 

"These numbers are going to continue to grow. We know that these confirmed numbers are just a small fraction of the individuals who are infected already in the state of Ohio," governor DeWine said during the press conference.

"We're told by medical experts that whatever the number is today, it will double in six days and that just continues on and on," he said.

Public health experts have rebuked US authorities for downplaying the pandemic and lagging far behind other hard-hit countries in rolling out testing for the virus.

As part of Ohio's measures to slow the spread of the coronavirus, Acton and DeWine signed an order banning most gatherings of more than 100 people. Ohio schools were also ordered to close for three weeks.

"We're all sort of waking up to our new reality," Acton said.

"The steps we're taking now will absolutely save lives."

Acton stressed the importance of slowing down the spread of the virus so that health services were not overwhelmed by a massive spike in cases.

"As we can see, we're in a crisis situation now," she said. 

"Taking decisive action now will greatly slow down this disease and stop this trajectory."

President Donald Trump has taken fire for what critics say is a slow response to the spread of the virus, which gives flu-like symptoms and has claimed more than 4,700 lives worldwide. 

He has repeatedly played down the threat, initially claiming that only a handful of Americans were at risk.

On Wednesday, Trump announced a ban on travel from mainland Europe as part of an "aggressive" effort to halt the spread of the pandemic.

The move, however, sent financial markets into a tailspin and sparked panic among stranded travelers.