China is dealing with the outbreak of a mysterious virus that has infected around 300 people and killed six, as well as travelling to other countries.
Authorities are fighting to stop it from spreading as millions travel for Chinese New Year, and scientists are trying to understand the virus, which has not been seen by humans before, and its effects.
The virus, called 2019-nCoV, is a coronavirus - which is one that infects the nose, throat, or sinuses - and has pneumonia-like symptoms. Experts say it can be spread from human to human.
Here's what we know:
A mysterious virus was first reported Chinese city of Wuhan in December 2019.
Chinese authorities launched an investigation in the first week of January, amid fears that the virus could be like to SARS — a virus that swept China and killed more than 700 people on the planet between 2002 and 2003.
But authorities later ruled that the virus is not SARS, even as more cases emerged. They said the virus had not been transmitted between humans.
It brings pneumonia-like symptoms including fever and difficulty breathing.
Health officials believe the virus originated in a seafood market in Wuhan, and they initially said that they believed the virus could only spread from animals to humans.
It was later identified as a coronavirus — which infects the nose, throat, and sinuses — referred to as the Wuhan virus, or 2019-nCoV.
As of January 21, the virus had killed six people,
China confirmed that around 300 people had been infected in the country as of January 21.
It said this included cases where the virus had spread to other parts of China, including Beijing, Guangdong province, Zhejiang province, Tianjin, and Shanghai.
State media reported that transport hubs in Wuhan have been set up with infrared thermometers to try and catch people that might have been infected — but this only started on January 14, potentially missing many people.
The number infected could be higher than what authorities have identified.
And one case has been recorded in South Korea, one in Japan, one in Taiwan, and two in Thailand — all from people from Wuhan or who had recently visited.
This map shows where cases have been confirmed, as of the morning of January 21.
The US Centers for Disease Control and Prevention are screening passengers arriving at three US airports from Wuhan.
It comes as the virus' spread could get much worse as hundreds of millions prepare to travel for the huge, weeks-long Chinese New Year holiday — a time referred to as the "largest annual human migration in the world."
China's National Health Commission said on Sunday that it will "step up our guard" and bring in new "control measures" in advance of the huge celebration.
The commission said on Sunday that it believes the virus is "still preventable and controllable."
The World Health Organization is figuring out how it should respond.
But for now, it is not recommending any sort of lockdown or end of movement: "Based on currently available information, WHO does not recommend any restriction of travel or trade."
Chinese President Xi Jinping said on January 20 that keeping people alive needed to be the "top priority" and the virus' spread "should be resolutely contained."