The chief of the World Health Organization (WHO) on Monday warned that the number of confirmed cases of coronavirus outside of China could be just the “tip of the iceberg.” 

WHO Chief Tedros Adhanom Ghebreyesus reportedly said at a briefing in Geneva that there had been “concerning instances” of transmission of the virus from people who had not been to China, where the virus originated in the city of Wuhan.

“The detection of a small number of cases may indicate more widespread transmission in other countries; in short, we may only be seeing the tip of the iceberg,” he said, according to Reuters. 

On Monday the death toll from the virus rose to 908, with all but two fatal cases in mainland China, according to Reuters. The other two deaths were in Hong Kong and the Philippines. 

Wu Fan, the vice-dean of Shanghai Fudan University Medical School, said the “situation was stabilizing,” when asked about the spread in Shanghai which has confirmed nearly 300 cases and one death, according to Reuters. 

The coronavirus has spread to at least 27 countries and territories, according to Reuters. 

The death toll has already surpassed that of SARS, which killed hundreds across the globe from 2002-2003. 

The Centers for Disease Control has confirmed 12 positive cases of the coronavirus in the U.S. as of Thursday.

The cases are confirmed in Arizona, California, Illinois, Massachusetts, Washington and Wisconsin.