Wuhan, a Chinese city of eleven million people, has temporarily shut down its public transport as it tries to halt the outbreak of a new strain of virus.
Those living in the city have been advised not to leave, in a week when millions of Chinese are travelling for the upcoming Lunar New Year holiday.
The respiratory illness has spread to other parts of China, with some cases in other countries including the US.
There are more than 500 confirmed cases and 17 people have died.
Known for now as 2019-nCoV, the virus is understood to be a new strain of coronavirus not previously identified in humans. The Sars (severe acute respiratory syndrome) virus that killed nearly 800 people globally in the early 2000s was also a coronavirus, as is the common cold.
All the fatalities so far have been in Hubei, the province around Wuhan.
Meanwhile, after a day of discussions in Geneva, the World Health Organization’s (WHO) emergency committee has announced it will not yet declare a “global emergency” over the new virus.
Director general Dr Tedros Ghebreyesus said more information was needed about the spread of the infection. The committee of health experts will meet again on Thursday.
A global emergency is the highest level of alarm the WHO can sound and has previously been used in response to swine flu, Zika virus and Ebola.
What measures have been announced?
From Thursday, all flights and passenger train services out of Wuhan have been stopped.
Bus, subway and ferry services all shut down from 10:00 local time (02:00 GMT).
A special command centre in Wuhan set up to contain the virus said the move was meant to “resolutely contain the momentum of the epidemic spreading”.
Those living in Wuhan had already been told to avoid crowds and minimise public gatherings.
State news agency Xinhua said tourist attractions and hotels in the city had been told to suspend large-scale activities while libraries, museums and theatres were cancelling exhibitions and performances.
A Lunar New Year prayer-giving ceremony at the city’s Guiyuan Temple, which attracted 700,000 people last year, has also been cancelled.
The hashtag “Wuhan is sealed off” was trending on Chinese social media website Weibo.
One user said worries about food and disinfectant made it feel like “the end of the world”, while another said they were on the “verge of tears” when Chinese officials announced the shut-down.
The WHO’s Dr Ghebreyesus described the latest measures as “very strong” and said they would “not only control the outbreak, they will minimise spread internationally”.
Chinese officials said the country was now at the “most critical stage” of prevention and control.
“Basically, do not go to Wuhan. And those in Wuhan please do not leave the city,” said National Health Commission vice-minister Li Bin in one of the first public briefings since the beginning of the outbreak.