Asia reported hundreds of new cases, Brazil confirmed Latin America's first infection and the new disease - COVID-19 - was also detected for the first time in Pakistan, Sweden, Norway, Greece, Romania and Algeria.
US health authorities, managing 59 cases so far - mostly Americans repatriated from a cruise ship in Japan - have said a global pandemic is likely.
President Donald Trump, who accused cable TV channels of exaggerating the danger and "panicking markets," is set to hold a news conference on Wednesday evening, a likely attempt to reassure markets and the public about the government's coronavirus response. It will be one of just a handful of times that the president has appeared in the White House briefing room.
Stock markets across the world have lost $3.3 trillion of value in four days of trading, as measured by the MSCI all-country index.
Wall Street reversed earlier gains on Wednesday afternoon and oil prices dropped to their lowest level in over a year, spooked in part by health officials saying dozens of people who had been in China were being monitored in suburbs of populous New York city - although no confirmed cases have been found.
New York Mayor Bill de Blasio urged the federal government to tighten testing for visitors from a range of countries where the virus has been spreading, adding added that its eventual detection in the city was "100% certain."
The virus that can lead to pneumonia is believed to have originated in a market selling wildlife in the central Chinese city of Wuhan late last year. It has infected about 80,000 people and killed more than 2,700, the vast majority in China.
While radical quarantining measures have helped slow the rate of transmission in China, it is accelerating elsewhere.
Germany, which has around 20 cases, said it was already impossible to trace all chains of infection, and Health Minister Jens Spahn urged regional authorities, hospitals and employers to review their pandemic planning.
The World Health Organization (WHO) said China had reported 412 new cases on Tuesday, while there were 459 in 37 other countries.
However, WHO chief Tedros Adhanom Ghebreyesus advised diplomats in Geneva on Wednesday against speaking of a pandemic - which the WHO defines as the worldwide spread of a new disease.
"Using the word pandemic carelessly has no tangible benefit, but it does have significant risk in terms of amplifying unnecessary and unjustified fear and stigma, and paralyzing systems," he said. "It may also signal that we can no longer contain the virus, which is not true."
The WHO says the outbreak peaked in China around Feb. 2, after measures that included isolating its epicenter Hubei province. It said only 10 new cases were reported in China on Tuesday outside Hubei.
FIRST LATIN AMERICAN CASE
Latin America's first case was in a 61-year-old man in Sao Paulo, Brazil, who had recently visited Italy, a new front line in the global outbreak.
The diagnosis coincided with the carnival holiday, a peak time for domestic travel. Brazil's stock index fell over 7%.
In addition to Brazil, Italians or people who recently visited Italy have tested positive in Algeria, Austria, Croatia, Greece, Romania, Spain, Sweden and Switzerland. Italy itself has reported more than 400 cases, centered on the industrial heartlands of Lombardy and Veneto.
A hotel in Tenerife in Spain's Canary Islands was locked down over cases linked to Italy.
"It's very scary because everyone is out, in the pool, spreading the virus," said 45-year-old hotel guest Lara Pennington.
In France, a second person died - a teacher who had not visited any country with a known outbreak.
In Japan, Prime Minister Shinzo Abe called for sports and cultural events to be scrapped or curtailed for two weeks to stem the virus as concern mounted for the 2020 Tokyo Olympics.
Japan has nearly 170 cases besides the 691 linked to the Diamond Princess cruise ship that was quarantined off its coast this month.
There have been nearly 50 deaths outside China, including 12 in Italy and 19 in Iran, according to a Reuters tally.
While Iran has reported only 139 cases, epidemiologists say the death rate of around 2% seen elsewhere suggest that the true number of cases must be many times higher.
Cases linked to Iran have been reported across the Middle East. Iraq imposed travel bans to affected countries and barred public gatherings.