Hong Kong authorities are stepping up efforts to curb the spread of the deadly H7N9 bird flu as millions of tourists from mainland China cross the city’s borders during the Labor Day holiday.

The government is doubling immigration and health officials at the border to screen around 4.2 million people expected to arrive to Hong Kong via crossing Shenzhen throughout the holiday, which runs from April 27 to May 1. Travelers will be scanned for raised body temperatures – a common symptom of H7N9.

The city has also stepped up patrols in poultry markets, Chief Secretary for Administration Carried Lam said.

The rare strain of bird flu virus spread to Taiwan where a man reportedly contracted the disease after returning home from a business trip to the Chinese city of Suzhou.

Meanwhile, experts are still determining whether the virus can be transmitted from person to person, raising fears that the outbreak could easily spread.

As of Saturday night, there were 120 confirmed cases of H7N9 in mainland China, mostly concentrated in the eastern coastal regions, Wall Street Journal reports.

The current scene is an unwelcome memory for Hong Kong; the densely populated city was ravaged by severe acute respiratory syndrome (SARS) in 2003, when 299 citizens died.