Hong Kong (CNN) -- Officials wielding infrared thermometers are becoming more difficult to avoid at entry points from mainland China as Hong Kong strengthens its defenses against the H7N9 strain of bird flu.
Extra measures are being taken this week during an expected surge in visitors across the border for the three-day Labor Day break from Monday to Wednesday.
Up to 600 officials will be stationed at border crossings during the holiday, including more than 100 volunteers in addition to government staff, according to Hong Kong's food and health secretary, Ko Wing-man.
"There will also be promotion and education work done at the borders reminding visitors to stay home or visit a doctor if they are not feeling well," he added, in response to reporters' questions on Sunday.
Along with extra screening at entry points, tour operators are also being asked to keep an eye on travelers who may be showing symptoms of what the World Health Organization calls "one of the most lethal influenza viruses" it has ever seen.
As of Sunday, the number of bird flu infections had risen to 124, based on provincial Ministry of Health websites. The figure includes one case in Taiwan, which remains the only recorded infection beyond mainland China.
Within the country, the infection has spread to eight provinces and the city of Shanghai, as well as the capital Beijing. Twenty-three people have so far died from the infection.
According to the last figures released from the national Ministry of Health on April 24, 14 people have recovered after treatment. On that day, the ministry switched to weekly updates and the figure hasn't been updated since.
Health authorities are still investigating the possible sources of infection and how the virus is spread. As recently as Thursday, the WHO repeated that so far there had been no evidence of sustained human-to-human transmission.
Taiwanese health officials say the territory's first case was imported by a local businessman who regularly traveled between back and forth between China's Jiangsu province and Taiwan.
To date, 27 cases have been reported in Jiangsu, resulting in four deaths. That's only the second highest number of provincial cases behind Zhejiang, which has reported 46 cases of infection and six deaths.
Wearing a customary white lab coat during a tour of the China's Center for Disease Control and Prevention on Sunday, Premier Li Keqiang urged officials to be vigilant against bird flu.
"We cannot afford to take it easy or relax, as we are facing a new virus. We should be prepared for any possible development," he said in quotes carried by state-run news agency Xinhua.
On Saturday, a mass cull was ordered at a major wholesale poultry market in the city of Dongguan after random testing detected the presence of an H7 strain of bird flu. No birds were showing symptoms, according to a statement from the city's Bureau of Agriculture. Nor had been there been any cases of human infection, it added. Dongguan is a city in the central province on Guangdong.
Hong Kong has said it is prepared to halt the import of live poultry, meat and eggs if the H7N9 virus is found at a mainland poultry farm with export ties to Hong Kong, or if that farm is within 13 kilometers of another that supplies the city.
CNN's Vivian Kam in Hong Kong and Feng Ke in Beijing contributed to this report.