"We don't fully understand it".
China on Thursday officially said that the number of confirmed cases of coronavirus infection has jumped by 3,694 to 28,018, the majority in and around Wuhan. The other fatalities were in Tianjin city, the northeastern province of Heilongjiang and Guizhou province in the southwest.
China has declared a "people's war" on the virus and the whole nation is working as one to combat it, Xi said.
More than two dozen airlines have suspended or restricted flights to China and hundreds of foreigners have been evacuated from Wuhan and placed in quarantine.
At least 20 people on the Diamond Princess - off Yokohama since Monday - have tested positive. Hong Kong leader Carrie Lam announced a 14-day quarantine of all travelers entering the city from the mainland starting Saturday, but the government has refused to seal the border entirely.
The World Health Organization announced that Wednesday was the first day the number of new cases was lower than the previous day's total.
China said it would halve tariffs on $75 billion worth of U.S. imports, as part of a trade truce with Washington and as officials look to calm markets unnerved by the outbreak.
China's fast-moving coronavirus spread among passengers of a quarantined Japanese cruise liner on Thursday and dragged down production at more global businesses, as scientists across the world searched for a vaccine. Malaysia and South Korea have confirmed three cases related to the meeting at the Grand Hyatt Singapore hotel, where four new cases have been discovered, bringing the city-state's total to 28.
India conducted the evacuation of its stranded citizen from Wuhan last week.
It is expected that the measure will further reduce cross-boundary flow of people between Hong Kong and the mainland, thus reducing the risk of transmission and spread of the disease in the community, the spokesman added. It is made by US biotech company Gilead Sciences.
And in Nanchang, the capital of Jiangxi province which borders Hubei, pharmacists must send reports to the authorities on anyone buying fever or cough medicine.
Global carmakers have already extended factory closures in China in line with government guidelines. Companies including Hyundai Motor, Tesla, Ford, PSA Peugeot Citroen, Nissan, Airbus, Adidas and Foxconn are taking hits.
Taiwan on Thursday confirmed two new cases of pneumonia caused by the coronavirus.
German sportswear company Adidas said it was temporarily shutting a "considerable" number of its stores in China.
A man is transferred from the World Dream cruise ship to an ambulance at the Kai Tak cruise terminal in Hong Kong on February 5, 2020, as health officials conduct inspections in the wake of the coronavirus outbreak across China.
European Central Bank President Christine Lagarde said the virus was adding to economic doubts.