The number of people killed in China by the coronavirus has risen to 81, with nearly 3,000 confirmed ill.
Tourist destinations are closed and school closings have been extended, in an effort to stop the spread of the virus.
The official end of the holiday will be postponed to Sunday from Friday to "effectively reduce mass gatherings" and "block the spread of the epidemic", a Cabinet statement said.
Making that task more hard is the fact that the virus can be spread before any symptoms appear, Chinese health authorities said Sunday, meaning carriers may not realize they are infected before they transmit the virus to others.
Australia confirmed its fifth case on Monday involving a woman on the last flight out of Wuhan to Sydney before China's travel ban.
The major US indexes gave up a significant amount of their gains for January on Monday and bond yields moved lower as investors headed for safer holdings.
Malaysia's government has announced it will ban travelers from the central Chinese city of Wuhan and other parts of surrounding Hubei province beginning immediately.
Other countries are in communication with Beijing to evacuate their nationals. France and Japan were weighing similar decisions.
The city, in China's Hubei province, has been put on lockdown with people trapped inside being prevented from leaving amid fears they could spread the virus.
The outbreak is a "notable downside risk" to growth, though it "could potentially be a high impact but short-lived event", said Tommy Wu and Priyanka Kishore of Oxford Economics in a report. The French government said it would fly its citizens to Wuhan in France and quarantine them there. Around 160 companies affiliated with Japan have offices in downtown Wuhan.
But after the pre-new year travel surge, the prospect of half a billion people getting back on trains, planes and buses and criss-crossing the country again is the last thing the government wants, he adds.
Wuhan, home to 11 million people, has been on virtual lockdown for days.
In Wuhan, construction workers raced against the clock to build two field hospitals within days to relieve overcrowded hospitals swamped with people waiting hours to see doctors overwhelmed by the influx.
Shanghai said on Monday that companies can not restart operations before February 9, and businesses in the eastern Chinese manufacturing hub of Suzhou have been ordered to stay shut until at least February 8. While a 48-year-old man is in hospital in Bordeaux, two others have been hospitalised in Paris.
Xinhua also said medical supplies are being rushed to the city, including 14,000 protective suits, 110,000 pairs of gloves and masks and goggles.
The virus is from the coronavirus family that includes the common cold but also more severe illnesses like SARS and Middle East Respiratory Syndrome.
The strain was isolated from environmental samples taken from the Huanan seafood market in Wuhan where the virus, known as 2019-nCoV, originated.
On China's heavily censored social media, officials have faced mounting anger over the virus, which is thought to have come from a market where wildlife was sold illegally.