The World Health Organization has declared the outbreak of a new virus from China a global emergency after the number of infected people spiked more than tenfold in a week.

The United Nations health agency made the determination on Thursday as more cases of human-to-human transmission were being reported worldwide.

To date, China has reported more than 7,800 cases, including 170 deaths.

Eighteen other countries have reported cases, as scientists race to understand how exactly the virus is spreading and how severe it is.