The new avian influenza A H7N9 virus gripping China has spread out to other parts of the country, yet disease experts continued to downplay an outbreak, claiming it still "is nothing out of the ordinary."

As of Sunday, the death toll has reached 13 while the number of infected have ballooned to 60.

But medical and disease experts from the World Health Organisation (WHO) said the increased numbers still remained quite ordinary.

"We've been expecting new cases to occur. ... Furthermore, we still expect that there will be other cases," Michael O'Leary, head of WHO's office in China, said.

The new avian influenza A H7N9 has likewise spread out from the original clusters in eastern China, including Zhejiang, Jiangsu and Anhui, as well as Shanghai. It has now reached Beijing and the central province of Henan.

"There's no way to predict how it will spread but it's not surprising if we have new cases in different places like we do in Beijing," Mr O'Leary told reporters in China.

But despite the growing death toll, number of infected and the seemingly transborder shift within the country, China's still has yet determine continued an indication of human-to-human transmission.

"That's a key factor in this situation," Mr O'Leary said. "As far as we know, all the cases are individually infected in a sporadic and not connected way."

"Investigations into the possible sources of infection and reservoirs of the virus are ongoing," the WHO announced. "Until the source of infection has been identified, it is expected that there will be further cases of human infection with the virus in China."

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