Hospital officials in Hong Kong raised their alert level to "serious" on Saturday as a mystery viral pneumonia outbreak in mainland China continued to spread.

The infection was first reported on Dec. 24 in Wuhan, a central Chinese city with a population of over 11 million. It has lead to online speculation about a resurgence of the flu-like SARS virus that killed hundreds of people in 2002-2003.

The number of reported cases has now risen from 27 to 44, with 11 people listed in serious condition, according to China's public health watchdog.

The outbreak sparked fears in Hong Kong when a woman who traveled to Wuhan during the Christmas holiday was admitted to hospital on Thursday for treatment of respiratory infections.

By mid-day, Saturday, Hong Kong's Hospital Authority had reported a total of eight cases to the city's health department.

Hong Kong's health and food secretary announced yesterday that seven more people were being treated.

Officials in the international financial hub also implemented enhanced monitoring and infection control in public hospitals and clinics.

In mainland China, authorities reported that the major cluster of recent infections have centered around a wet market in Wuhan where wild animals were sold.

They were still in the process of identifying the cause, but have determined that common respiratory diseases such as influenza, bird flu, and adenovirus infection are not to blame.

So far, Chinese officials say there has been no human-to-human transmission, but Ho Pak-Leung, director of the University of Hong Kong's Center for Infection, advised the city to brace for that possibility.