The number of human H7N9 bird flu infections continues to rise nationwide with about 20 new cases reported in the first two weeks of 2014.

On Wednesday, three new H7N9 cases were reported from Shanghai and Fujian and Zhejiang provinces.

Since Jan 1, Shanghai has reported four cases, including a 35-year-old man from Ningbo, Zhejiang province, on Wednesday.

In Fujian province, a man surnamed Lin, 50, from JinJiang, was in serious condition and receiving treatment at a local hospital, health authorities said.

Zhejiang province has reported new cases for seven consecutive days. As of Wednesday, the eastern province had reported 12 cases, including some fatalities.

The latest on Wednesday was a 41-year-old male farmer from Yuhang in Hangzhou, the provincial capital.

Zhejiang was also the site of China's first confirmed human-to-human transmission last November, when a man was infected while caring for his father-in-law, according to Xinhua News Agency.

About 150 cases of H7N9 bird flu have been confirmed in China since the first case in March last year, health authorities said.

The virus is more active in winter and spring, and high-density transportation on buses, trains and planes could create "favorable circumstances" for the virus to spread, said Li Lanjuan, China's leading bird flu researcher and member of the H7N9 prevention and control group.

Li also warned the virus might be spread by migrants returning to their mainly rural homes from developed eastern regions for Spring Festival.

Southern China has seen a high occurrence of the H7N9 virus and prevention should be intensified, especially to avoid contacts with live poultry, a health official said after a number of human infections of the bird flu were reported recently.

"Most of these confirmed patients had contact with live poultry. Preliminary virus tests didn't find any variation. And there is no evidence the virus was spread among humans," Feng Zijian, director of the health emergency center at the Chinese Center for Disease Control and Prevention, told China National Radio.

On Monday, southern China's Guangdong province reported two separate cases in Nanhai district of Foshan.

The district has reported six cases, the most in the province.

Of the two cases, a 46-year-old driver who raises live birds at his home fell ill on Jan 6 and is now in critical condition. In the other case, a 28-year-old who sells birds fell ill on Jan 8 and is in stable condition.

The Nanhai district government closed live-bird markets in the district on Monday and Tuesday.

So far, 16 human cases of the H7N9 virus have been reported in Guangdong province since the first reported case in Huizhou in August.

The article was originally published on China Daily.

Xinhua and Xu Jingxi contributed to this story.