Vietnam has announced an immediate ban on all Chinese poultry imports and stepped up border controls after its northern neighbour reported two deaths from a new strain of bird flu.

There have been seven human infections -- two fatal -- in China from the virulent disease, according to local authorities, the first time the H7N9 strain of avian influenza is known to have been transmitted to humans.

Hanoi has imposed the ban to "actively and efficiently prevent the intrusion of the H7N9 virus into Vietnam", according to an urgent message signed by the Minister of Agriculture Cao Duc Phat.

The ban was effective immediately, according to the notice which was posted on the ministry's website late Tuesday.

Chinese authorities are trying to determine how exactly the new variety of bird flu infected seven people, but say there is no evidence yet of human-to-human transmission.

In Shanghai, where two people have died from the virus, some residents expressed worries on Wednesday over eating poultry.

At a traditional food market in downtown Shanghai, one middle-aged woman shunned the freshly-plucked chickens and duck necks on display.

"I'll stop buying chickens for the moment and wait until the situation eases," she said.

Shanghai officials have assured people that the city's chicken and pork are safe to eat, after the H7N9 cases and the recovery of more than 16,000 dead pigs from the city's main river last month, but many are unconvinced.

"I don't dare eat fowl or chicken. I'm going to be a vegetarian," said a Shanghai resident posting on a microblog under the name Miss Muyisi.

Imported poultry from China -- both legal and smuggled across the 1,350 kilometre (850 mile) land border -- is commonly found in Vietnam's markets.

Thousands of live chicks and tonnes of chicken from China have been confiscated by Vietnamese border authorities over the past few days, according to the ministry's notice.

Last year two people died in Vietnam from the more common strain of avian influenza, H5N1.

According to the World Health Organization (WHO), Vietnam has recorded one of the highest numbers of fatalities from bird flu in southeast Asia, with at least 59 deaths since 2003.

H5N1 has killed more than 360 people globally from 2003 until March 12 this year, according to the WHO.

It said there was no evidence so far of human to human transmission between the confirmed H7N9 cases in China, or among their contacts, but added it was crucial to find out how the virus infected humans.

The official Vietnam News Agency said Wednesday the H5N1 strain of virus is currently under control in the country. The government has approved purchase of 40 million doses of bird flu vaccines to prevent outbreaks.

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