The World Health Organization (WHO) has urged the global populace to refrain from panicking over the new bird flu pandemonium in China even as the number of infected has added four new cases on Tuesday, taking the total of reported cases now to seven.

"It is of concern to WHO and we will be following this with the health authorities in China to know more. But for the time being, it's only seven cases and it has shown, for the time being, no human-to-human transmission," Fadela Chaib, UN health agency's spokeswoman, told reporters on Tuesday.

She admitted, however, that they are appalled as to how the virus was able to infect humans, noting it is now crucial to find how this became so.

"It's the first time that H7N9 was found in humans," Ms Chaib pointed out.

On Tuesday, four more people in east China's Jiangsu Province have been confirmed infected with the H7N9 bird flu. According to a government Web site that cited the authorities in the city of Nanjing, in Jiangsu Province northwest of Shanghai, the four new patients were aged 32 to 83, have been sent to the hospitals and are all critically ill.

Over the weekend, two men aged 87 and 27, died in early March in Shanghai after being infected with the lesser-known H7N9 avian influenza. However, it was only on Friday that confirmation was released of the presence of the virus in the victims.

A 35-year-old woman in the eastern province of Anhui, near Shanghai, is now being monitored and is also in critical condition with the virus.

If for any consolation, the cases seem to bear no correlation with each other.

"To date the investigation showed no link between the three cases, but the investigation is still ongoing,' Ms Chaib said. She noted the 88 individuals with whom the victims had been in contact with are also being monitored.

WHO likewise stressed that H7N9 could not easily be contracted by humans, although one of the four people in Nanjing infected is a poultry butcher.

"This is of concern," Gregory Hartl, a WHO spokesman, was quoted by Bloomberg. "These are the first cases we've seen in human beings. We're watching this very closely."

Meantime, China has launched a nationwide screening programme for the rare but lethal strain.

The government of Shanghai has likewise announced a level-3 flu alert on Monday. Xu Jianguang, chief of Shanghai's health and family planning commission, said at a briefing on Tuesday that municipal health authorities will strengthen monitoring of influenza as well as report daily pneumonia cases where causes are unknown.

There are no available vaccines against the H7N9 bird flu virus.

China has urged its citizens to refrain eating wild poultry.