According to China's health commission minister:

“The transmissibility shows signs of increasing and the ‘walking source of infection’ [where patients have few signs of disease] has made it difficult to control and prevent the disease,” said Ma Xiaowei.

“For this new coronavirus we have not identified the source of the infection and we are not clear about the risk of its mutation and how it spreads. 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.”

Sounds a bit alarming.