A rapidly spreading viral outbreak is disrupting travel and business in China, which has taken unprecedented steps to lock down cities with a combined 40 million people around the epicenter in Wuhan to try to slow its progress.

For global corporations, Wuhan is an important hub. Of about 2,000 cities in China with factories and other facilities in Bloomberg's supply chain database, the city ranks 13th, with about 500 facilities.

The province of Hubei has 1,016, making it seventh of 32 such jurisdictions. U.S.-based companies have 44 facilities there, and European ones about 40, the data show. Many plants are in the auto and transportation industries, and big names include PepsiCo. Inc. and Siemens AG.