Developments in the coronavirus crisis have escalated rapidly, with U.S. officials declaring the outbreak a public health emergency on Friday, following the World Health Organization characterizing the virus’ spread as a growing risk to global economies.

The U.S.’s warning came a day after it issued a travel advisory to China, and as multiple airlines have sharply curtailed or suspended flights to the world’s second largest economy — which is reeling as the death toll spikes to over 200 amid more than 9,800 infections. In addition, the U.S. also slapped mandatory travel and quarantine restrictions on Americans and foreign nationals that have recently visited China.

On Friday, United Air (UAL), American Airlines (AAL) and Delta (DAL) all announced plans to suspend all U.S.-China flights starting next week.

Though it is not as deadly as SARS outbreak, the coronavirus has outpaced the 2002-2003 spread of SARS. WHO officials say 99% of the cases are contained to mainland China, but new cases have popped up around the world — including in the United Kingdom, which on Friday reported its first confirmed cases.

Fears about the economic spillover in an uncertain global growth environment are unnerving investors, even as the WHO stopped short of calling for an outright travel ban. Goldman Sachs estimated on Friday that the virus wold cut China’s growth by a 1/4 of a percentage point this year, with a commensurate drag on annualized U.S. first quarter growth.

Tedros Adhanom Ghebreyesus, the WHO’s Director-General, said on Thursday that “there is no reason for measures that unnecessarily interfere with international travel and trade.” However, he acknowledged it could spread to countries “with weaker health systems [that] are ill-prepared to deal with it.”

View photos The number of coronavirus cases that have surfaced around the world, as of Jan. 31. More

Markets

Virus fears walloped Wall Street on Friday, as investors took fright over simmering fears of a global pandemic — and how it could affect growth. The S&P 500 (^GSPC), Dow (^DJI) and the Nasdaq (^IXIC) all plunged in Friday’s trading, reversing most if not all of 2020’s heady gains. Sentiment was already curdled by the Centers for Disease Control’s announcement on Thursday that the U.S. had seen its first human-to-human coronavirus infection.

With travel and leisure stocks already under pressure, Delta, American and United all saw their shares tumble by at least 2% each after announcing they would suspend their China flights.

Asian markets, which were closed for part of the week for the Lunar Year holiday, have been under pressure, as have travel and leisure companies that may bear the initial brunt of reduced travel.

View photos A television screen headlines trading on the floor of the New York Stock Exchange, Monday, Jan. 27, 2020. Stock tumbled at the open on Wall Street following a sell-off in markets in Europe and Japan as investors grow more concerned about the potential economic impact of an outbreak of a deadly coronavirus. (AP Photo/Richard Drew) More

Businesses have taken action in the meantime, with reports of empty streets in parts of China and Hong Kong as some large employers close offices and ban travel. Some of the companies affected include Starbucks (SBUX), McDonalds (MCD), Microsoft (MSFT), Google (GOOG), Tesla, IKEA and Toyota.

Travel

Even before the U.S. travel advisory, some major airlines chose to reduce or suspend flights to China as a precautionary measure. On Thursday, the American Airlines pilot’s union filed a lawsuit minutes after the announcement to halt all future flights to China, citing concerns over the ease of the spread of the disease.