China's deadly coronavirus is becoming more infectious and carriers of the disease can pass it on even if they show no symptoms, China’s National Health Commission warned on Sunday.

Nearly 2,000 people in China have been infected and 56 killed by the disease, which originated in the city of Wuhan. Cases have now been reported across the globe, including in Thailand, Australia, the United States and France.

“The transmissibility shows signs of increasing and the ‘walking source of infection’ [where patients show little sign of disease] has made it difficult to control and present the disease,” Minister Ma Xiaowei, told a packed press conference in Beijing.

The source of the infection had not yet been identified, and “we are not clear about the risk of its mutation and how it spreads,” he added. “Since this is a new coronavirus there might be some changes in the coming days and weeks, and the danger it poses to people of different ages is also changing.”

The coronavirus, which began in a seafood market in Wuhan, Hubei province, has since spread to every region of China, bar Tibet. Wuhan, a city of 10 million, has been completely sealed off and severe travel restrictions have spread to 14 other cities over the weekend, corralling close to 60 million people.