New coronavirus has now reached more than 20 countries from China, where the epidemic or disease outbreak began over a month ago.
Experts are worried about how much further it could spread and how many people will get sick.
A truly global outbreak or pandemic has not been declared yet.
But officials are preparing for the possibility that this could be the next pandemic that the world will have to face.
What is a pandemic?
The description is reserved for an infectious disease threatening lots of people all over the world simultaneously.
A recent example was the 2009 swine flu pandemic, which experts think killed hundreds of thousands of people.
Pandemics are more likely if a virus is brand new, able to infect people easily and can spread from person to person in an efficient and sustained way.
Coronavirus appears to tick all of those boxes.
With no vaccine or treatment that can prevent it yet, containing its spread is vital.
When is a pandemic declared?
According to the World Health Organization's (WHO) description of pandemic phases, coronavirus is only a step away from being a pandemic.
It is spreading between people and has been seen in many of China's neighbouring countries, as well as further afield.
If we start seeing sustained community-level outbreaks in multiple parts of the world, then it will be a pandemic.
How likely is that?
It is still unclear how severe the disease is, and how far it will spread.
WHO's Director-General Dr Tedros Adhanom Ghebreyesus says the spread outside of China so far appears to be "minimal and slow".
There have been more than 17,000 confirmed coronavirus cases and around 360 deaths, mostly in China.
Outside China, there are more than 150 confirmed cases of the virus - and one death, in the Philippines.
"If we invest in fighting at the epicentre, at the source, then the spread to other countries is minimal and also slow," Dr Ghebreyesus told a WHO executive board meeting on Monday.
Each pandemic is different and, until a virus starts circulating, it is impossible to predict its full effects.
Experts suspect that coronavirus may be less deadly than some other recent disease outbreaks, such as Sars.
The decision by the World Health Organization to declare the situation a Public Health Emergency of International Concern (PHEIC) was taken primarily because of the signs of human-to-human transmission outside China, and what might happen if the virus were to spread in a country with a weaker health system.
WHO says although countries should take steps to prevent and limit further spread of the virus, there is no reason yet for measures which unnecessarily interfere with international travel and trade.