The new coronavirus outbreak "is a controllable pandemic" if countries step up measures to tackle it, the head of the World Health Organization said on Thursday.

WHO Director General Tedros Adhanom Ghebreyesus acknowledged the global outbreak of the new coronavirus could now be considered a pandemic - a disease actively spreading globally.

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But he told diplomats in Geneva that describing the contagion as a pandemic should not mean countries give up the fight to stop it from spreading further.

"This is a controllable pandemic," he said. "We are deeply concerned that some countries are not approaching this threat with the level of political commitment needed to control it.

"The idea that countries should shift from containment to mitigation is wrong and dangerous," he stressed.

More than 4,600 people have died, while the WHO said there are 126,000 cases in over 100 countries.

"To save lives we must reduce transmission," Tedros insisted. "That means finding and isolating as many cases as possible and quarantining their closest contacts."

He urged states to test every suspected case of COVID-19 in a bid to slow transmission.

"Even if you cannot stop transmission, you can slow it down and protect health facilities, old-age homes and other vital areas - but only if you test all suspected cases."

The majority of cases have been in China, where the virus emerged in December, but major hot spots have also arisen in South Korea, Iran and Italy.

Together, those four countries account for more than 90 percent of all reported cases, according to the WHO.

'Robust surveillance'

The pandemic has disrupted cultural and sporting events around the world as authorities try to prevent large gatherings.

Tedros said countries needed to find the right balance between protecting health and preventing social and economic disruption.

However, "containment" needs to remain the central pillar in any plan to tackle the spread, he said.

"You can't fight a virus if you don't know where it is. That means robust surveillance to find, isolate, test and treat every case, to break the chains of transmission."

Tedros urged unaffected countries to prepare their health facilities, and pressed all states to innovate and share any new ways to prevent infections and minimise the impact of the outbreak.

More than $440m has been pledged towards the WHO's strategic preparedness and response plan, he added.