FACTBOX-What we know about the coronavirus spreading in China and beyond

An outbreak of a new coronavirus that began in the central Chinese city of Wuhan has killed 17 and infected nearly 650 people globally. Health authorities fear the transmission rate will accelerate as hundreds of millions of Chinese travel at home and abroad during the week-long Lunar New Year holiday that begins on Saturday.

The virus has caused alarm because it is still too early to know just how dangerous it is and how easily it spreads between people. Because it is new, humans have not been able to build an immunity to it. Here is what we know so far:

* Chinese state television reported on Thursday there were 634 cases in China. Authorities have confirmed 17 deaths. * The previously unknown strain is believed to have emerged late last year from illegally traded wildlife at an animal market in Wuhan.

* Thailand has reported four cases, and South Korea, Japan, Taiwan, and the United States one each. Patients in these cases were either residents of Wuhan or recent visitors to the city. * Singapore confirmed its first case on Thursday - a Chinese resident of Wuhan; an Indian nurse working in Saudi Arabia was confirmed infected; two Chinese citizens in Vietnam have tested positive.

* Symptoms include fever, cough and difficulty breathing. * China says the virus is mutating. It says there is evidence of respiratory transmission.

* Three research teams are to start work on developing potential vaccines, the Coalition for Epidemic Preparedness Innovations said. The plan is to have at least one potential vaccine in clinical trials by June. * Preliminary research suggests the virus was passed to humans from snakes, but Chinese government medical adviser Zhong Nanshan has also identified badgers and rats as possible sources.

* Wuhan, a city of 11 million people, is on lockdown, with urban transport shut and outgoing flights suspended. * Nearby Huanggang, a city of 7 million people, is suspending public transport and closing venues, including movie theatres and internet cafes.

* Beijing closed tourist access to the Forbidden City and canceled large gatherings, including two Lunar New Year temple fairs. * Airports around the world have stepped up screening of passengers.

* The World Health Organization will decide on Thursday whether to declare the outbreak a global health emergency, which would step up the international response. * World shares fell on Thursday, led by the biggest decline in Chinese stocks in more than eight months, as concern mounted about the spread of the virus.

(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)