The world has entered uncharted territory in its battle against the deadly coronavirus, the UN health agency warned, as new infections dropped dramatically in China on Tuesday but surged abroad with the US death toll rising to six.

Globally, the virus has killed more than 3,100 people and infected over 90,000 even as a clear shift in the crisis emerges, with nine times as many cases recorded outside China as inside, according to the WHO.

China has imposed draconian quarantines and travel restrictions to keep large swathes of the population indoors for weeks, a strategy that appears to have paid off as new cases have been falling this month.

While Italy has locked down towns, other countries have stopped short of imposing mass quarantines and instead have discouraged large gatherings, delayed sporting events and banned arrivals from virus-hit nations.

South Korea, Iran and Italy have emerged as major COVID-19 hotspots, which is believed to have started at a market that sold wild animals in the central Chinese city of Wuhan late last year.

South Korea, the biggest cluster outside China, approached 5,000 cases on Tuesday as 477 new infections were reported, with two more fatalities taking its death toll to 28.

"The entire country has entered a war with the infectious disease," South Korean President Moon Jae-in said.

China is even importing infections now, with 13 so far, including eight Chinese nationals who had worked at the same restaurant in northern Italy's Lombardy region.

"We are in uncharted territory," WHO chief Tedros Adhanom Ghebreyesus said. "We have never before seen a respiratory pathogen that is capable of community transmission, but which can also be contained with the right measures."

Community transmission means infections within a population are not imported from another virus-hit area.

The United States is now facing a potential epidemic, with six people dying in the northwestern state of Washington, where officials warned residents the battle against the disease was shifting from containment to mitigation. 

"The risk for all of us of becoming infected will be increasing," said Jeff Duchin, a health officer in King County where five of the deaths occurred. 

The county has more than two million residents and is home to Seattle, a major commercial and transportation hub in the Pacific Northwest region.

- US eyes treatment -

The White House, which has been accused of downplaying the threat from the virus, continued to strike a bullish tone.

Vice President Mike Pence declared that a treatment "could literally be available by this summer, or early fall".

He was likely referring to remdesivir, an antiviral drug developed by the pharmaceutical firm Gilead that has already been used to treat one US patient and was moving toward two expansive final stage trials in Asia.

Pence also announced American pharmaceuticals were forming a consortium to fight the virus, and that South Korea and Italy would screen all their airline passengers bound for the US.

Despite its world-class hospitals and cutting-edge research, the US is viewed as vulnerable to an epidemic because of glaring disparities in healthcare availability, with nearly 28 million people without coverage.

- China cases down -

China reported 125 new cases on Tuesday, its lowest daily increase in six weeks, with all but 11 infections in Hubei province, of which Wuhan is the capital. The nationwide death toll rose to 2,943 with 31 more deaths, all in Hubei.

Chinese officials have touted progress in the battle against the epidemic, which has hammered the world's second-largest economy and threatened to cut into global growth.

Stock markets tanked last week but rebounded on Monday after governments and central banks said they would step in if needed to soften the blow.

Australia's central bank slashed interest rates to a record low on Tuesday.

Finance ministers and central bank chiefs from G7 countries will hold talks on the issue on Tuesday.

- Hotspots elsewhere -

UN medical experts arrived in Iran on Monday to help tackle the world's second-deadliest coronavirus outbreak, with 66 fatalities and more than 1,500 infections.

China has also sent experts to Iran, while Germany, France and Britain have pledged emergency medical supplies including testing equipment, body suits and gloves.

In Italy, tourist hotpots including the Duomo in Milan reopened to visitors but access was limited to avoid overcrowding.

Italy, Europe's worst-affected country with around 1,700 infections, said Monday its deaths from the virus had jumped 18 to 52.

The WHO says the virus appears to particularly hit people over the age of 60 and those already weakened by other illnesses. 

Its mortality rate is between two and five percent -- higher than the seasonal flu.

Canada asked travellers arriving from Iran - one of the countries hardest hit by the new coronavirus epidemic - to self-isolate at home for 14 days, even if they are not exhibiting any symptoms.

Health authorities asked Canadians to avoid any non-essential travel to Iran and the northern region of Italy, which have both emerged as major hotspots for the infection. 

The respiratory illness has killed 66 people in Iran with more than 1,500 confirmed infections.

Many cases in Canada had been linked to the Iran outbreak, Canadian chief medical officer Theresa Tam told reporters. Canada had 27 confirmed cases of COVID-19 infection as of Monday evening.

Latest developments worldwide

- World spread -To date, more than 3,100 have died from the new virus, while more than 90,000 have been infected in 73 countries and territories around the world, according to AFP's latest toll based on official sources at 0600 GMT Tuesday.

Mainland China, excluding the semi-autonomous territories of Hong Kong and Macao, has 80,026 cases, including 2,943 deaths. Elsewhere in the world, 10,134 cases and 166 deaths have been recorded.

China reports an increase in cases coming from abroad, as the country where the disease first emerged now worries about importing infections.

South Korea remains the hardest-hit country after mainland China, with 4,335 cases and 28 deaths, followed by Italy (2,036 cases and 52 deaths), Iran (1,501 cases and 66 deaths) and Japan (254 cases, 12 deaths). More than 700 cases have been registered on the Diamond Princess cruise ship anchored off Japan.

In Germany the number of infected people has almost doubled over the weekend, reaching 157.

France, another coronavirus hotspot in Europe, has registered some 130 people infected since late January, three of whom have died.

The 27-nation EU raised the coronavirus risk to "moderate to high".

Andorra, the Czech Republic, Indonesia, Portugal, Saudi Arabia and Senegal confirm their first cases.

- OECD lowers growth forecasts -

The OECD lowers its global growth forecast for 2020 by half a percentage point to 2.4 percent, the worst performance since the 2008 crisis.

In China, annual economic growth is expected to reach just 4.9 percent, a 0.8 point drop from the OECD's original growth forecasts announced last November.

EU Commissioner Thierry Breton says the EU's tourism sector has lost around a billion euros per month since January and warns of a risk of recession in Germany and Italy. 

Australia's central bank slashes interest rates to a record low and says it is ready to take further action to support the economy if needed.

In the Chinese enclave of Macao, casinos announce a fall in gaming revenue of nearly 88 percent in February.

- Global measures -

In South Korea, subject to travel restrictions by more than 70 countries, dozens of major events are cancelled.

Hong Kong postpones its Vinexpo trade fair from May to July.

A sixth person dies in the northwestern US state of Washington and President Donald Trump faces criticism over his administration's preparedness.

A plane carrying UN medical experts and aid touches down in Iran on a mission to help it tackle its outbreak, as European powers say they will send further help.

The Louvre in Paris, the world's most visited museum, is closed for a second day running after staff again refuse to work. 

In Israel, where legislative elections are taking place, special polling stations are set up for more than 5,000 Israelis under quarantine.