Cao Duc Phat, who also heads the Ministry of Agriculture and Rural Development, sent an instructional message nationwide after the virus reportedly re-hit northern Vietnam, first in Hai Duong province on February 14, and then Ha Tay and Hanoi.

He warned that many provinces have so far concentrated only on vaccinating their fowl flocks against the disease but have neglected other preventive measures.

In the message, Mr Phat said "vaccination is only one of many essential measures to combat bird flu."

Comprehensive measures were outlined, including monitoring all poultry-raising households, especially egg-hatching farms, and minimizing the contact of poultry with migrating birds.

Farmers were asked not to raise chickens with waterfowl and other farm animals and to isolate live poultry bought in markets from their existing flocks.

The Committee Head also asked for regular disinfection of poultry farms, slaughterhouses, poultry processing establishments, live birds markets, high-risk areas and former bird flu-affected spots.

Quarantine officials were told to intensify their control over the transport, slaughtering, and trading of poultry and poultry products.