The death toll from a mysterious flu-like virus in China climbed to six on Tuesday as new cases surged beyond 300 and authorities fretted about the added risk from millions of Chinese traveling for the Lunar New Year holiday.

Round the world, airports tightened the screening of travelers from China as officials confirmed the coronavirus strain is contagious between humans. The World Health Organization (WHO) called a meeting for Wednesday to consider declaring a global health emergency. The outbreak, which began in the central city of Wuhan, also sent shivers through financial markets as investors recalled the fallout from China’s Severe Acute Respiratory Syndrome (SARS) outbreak in 2002/2003 that it initially covered up. The SARS coronavirus killed nearly 800 people then.

There have been six deaths in that city, Mayor Zhou Xianwang told Chinese state television on Tuesday. The virus has been spreading around other parts of China, however, including five cases in the national capital Beijing. Fifteen medical personnel are among those infected. The WHO’s regional director for the western Pacific, Takeshi Kasai said Information about the newly reported infections suggest there may now be sustained human-to-human transmission