In 2002, when a lethal, pneumonia-like virus known as SARS emerged in China, the country’s factories were mostly churning out low-cost goods like T-shirts and sneakers for customers around the world.

Seventeen years later, another deadly virus is spreading rapidly through the world’s most populous country. But China has evolved into a principal element of the global economy, making the epidemic a substantially more potent threat.

The outbreak of the virus in Wuhan, a city of 11 million people, prompted the Chinese government to effectively quarantine the metropolis and much of surrounding Hubei province, barring people from moving around.

International companies that rely on Chinese factories to make their products and depend on Chinese consumers for sales are already warning of costly problems.

Apple, Starbucks and Ikea have temporarily closed stores in China. Shopping malls are deserted, threatening sales of Nike sneakers, Under Armour clothing and McDonald’s hamburgers. Factories making cars for General Motors and Toyota are delaying production as they wait for workers to return from the Lunar New Year holiday, which has been extended by the government to halt the spread of the virus. International airlines, including American, Delta, United, Lufthansa and British Airways, have canceled flights to China.

Until now, the impact on factories was limited by the fact that the outbreak was unfolding during the Lunar New Year, the most important holiday of the year. Many businesses are closed during the holiday, while hundreds of millions of migrant workers return home to their families in the countryside.

In a bid to keep people home and halt the spread of the virus, the government extended the holiday three days. But the fear of the virus is so widespread and intense that many workers are likely to remain away from factory towns for at least a week.