Three Chinese people have died of the H7N9 bird flu, the state news agency Xinhua said on Tuesday, adding to a spike in cases this year.

Two men, ages 76 and 52, died in southern Guangdong province on Monday, while a third patient passed away in eastern Jiangsu province on Saturday, Xinhua said in separate reports, citing provincial health authorities.

Two new cases were also reported -- a four-year-old girl in Guangdong in stable condition, and a 59-year-old woman in Jiangsu in critical condition.

So far this year China has confirmed 115 human H7N9 cases, including 25 deaths, according to an AFP tally of reports by local authorities.

By comparison in 2013 there were 144 infections and 46 deaths, according to official figures.

The World Health Organization (WHO) said last week that the rise in cases this year was not surprising due to seasonal factors, rather than a virus mutation.

The same week Hong Kong was forced to cull up to 20,000 chickens after finding H7N9 present in poultry imported from mainland China, days before the Lunar New Year celebrations.

Mainland China's H7N9 outbreak among humans began in February 2013, triggering concerns that the virus could mutate to become easily transmissible among people, potentially triggering a pandemic.

Both Chinese authorities and the WHO have said there has been no evidence so far of sustained human-to-human transmission.

But limited spread - such as among relatives who have been in close contact - is possible. Last week a couple and their daughter contracted the H7N9 bird flu eastern Zhejiang, China's worst-hit province, Xinhua reported at the time.