GUANGZHOU -- The number of H7N9 human cases in South China's Guangdong province has climbed to 50, with one new case reported on Friday, local health authorities said Saturday.

A 45-year-old man from Meijiang district in Meizhou city was diagnosed with the disease Friday. He was in critical condition, the provincial health and family planning commission said in a press release.

Bird flu is most likely to strike in winter and spring.

In Guangdong Province, H7N9 human cases have been reported in 15 of all the 21 prefecture-level cities and 12 people have died. Thousands of chickens have been culled and live poultry trade has been banned in several cities.

Though the disease could be fatal, experts say patients could suffer less if they take the anti-viral drug oseltamivir in time.

"We found patients who took oseltamivir on the first day they had flu-like symptoms often recovered quickly, while those who waited until the seventh day often ended up on the critical list," said He Jianfeng, a chief specialist with the provincial disease prevention and control center.

He said all flu patients are advised to take oseltamivir, which cuts most flu symptoms and can help some patients avoid hospital treatment and complications.

Local health authorities have demanded all hospitals to stockpile the anti-viral, as flu outbreak is likely to last until May.

Other Chinese localities including Shanghai, Fujian, Jiangxi, Guizhou and Zhejiang have also reported human cases of H7N9 this winter.

H7N9 is a bird flu strain first reported to have infected humans in March 2013.