Wuhan | Zhang Qi was planning to spend a week of leisure in Wuhan when he arrived on January 21. It looked like any other day in the historic, prosperous central China metropolis of 11 million people.

That sense evaporated in the evening as Zhang watched renowned epidemiologist Zhong Nanshan issue a sobering warning in a television interview. A new form of viral pneumonia was showing signs of spreading among people in the city and had already sickened a number of medical workers, Zhong said.