The US state department has issued a new advisory warning Americans against all international travel in an effort to combat the coronavirus pandemic.

The top-level "do not travel" warning usually applies to the most high-risk countries around the world. Its application to all international travel represents a significant step in Washington’s efforts to stop the spread of the virus.

The measure calls on all Americans abroad to return to the US or prepare to be stranded where they are.

"The Department of State advises US citizens to avoid all international travel due to the global impact of Covid-19," said a statement. "In countries where commercial departure options remain available, US citizens who live in the United States should arrange for immediate return to the United States, unless they are prepared to remain abroad for an indefinite period."

The top-level warning was previously in place for only 15 countries, including China, Iran, Syria and Afghanistan. China was added to the list in January amid concerns about the coronavirus.

President Donald Trump had earlier declined to confirm or deny that report at a midday news briefing, saying only that he was planning to meet with State Department officials later on Thursday.

"We haven't had the meeting yet," he said.

More than 10,000 people across the United States have been diagnosed with the illness called Covid-19 and more than 160 have died, with the largest numbers so far in Washington state and New York.