A two-member advance team of World Health Organization experts has left for China to organise an investigation into the origins of the novel coronavirus behind a pandemic that has killed more than 550,000 people globally, the United Nations agency said on Friday. World Health Organization said in its latest description that the virus transmission by aerosols may have been responsible for outbreaks of COVID-19 reported in "Some closed settings, such as restaurants, nightclubs, places of worship or places of work where people maybe shouting, talking or singing".

This comes a day after it acknowledged the emerging proof of airborne spread of the virus after an open letter by over 200 scientists outlined evidence that showed floating virus particles can infect people who breathe them in.

The coronavirus pandemic, which has not yet peaked in many parts of the world, has exposed weaknesses and left billions of people without reliable and affordable access to essential health services, he said. "This is a question we all need answered", Harris told a news briefing.

Initially the body refused to recommend the use of face masks.

The World Health Organisation has changed its stance on whether coronavirus can be spread through the air.

"We know it's very, very similar to the virus in the bat, but did it go through an intermediate species?" Droplets typically drop to the ground soon after they leave the mouth or nose of an infected person.

"In these outbreaks, aerosol transmission, particularly in these indoor locations where there are crowded and inadequately ventilated spaces where infected persons spend long periods of time with others, can not be ruled out", it added.

The worst hit country, the U.S., is approaching the grim milestone of nearly one in every hundred people infected with Covid-19.

As of Saturday, the total number of global coronavirus cases stood at 12,507,849, while the fatalities rose to 560,460, according to the Johns Hopkins University.

Airborne transmission occurs when someone inhales virus-containing aerosols, or small floating particles, that can linger in the air for some amount of time.

The WHO has maintained that current evidence suggests that transmission of SARS-CoV-2 occurs primarily between people through direct, indirect, or close contact with infected people through infected secretions such as saliva and respiratory secretions, or through their respiratory droplets, which are expelled when an infected person coughs, sneezes, talks or sings.

Diseases that have been found to spread through aerosols include measles and tuberculosis.

WHO Director-General Tedros Ghebreyesus has warned coronavirus is accelerating out of control globally.