HANOI, June 4 (Reuters) - Bird flu spread to three duck farms in Vietnam"e;s central and southern regions last week, killing more than 300 waterfowl, the government said on Monday.

Two duck farms in the southern Mekong delta province of Dong Thap lost 224 ducks last Friday, while 95 ducks died in the central province of Quang Nam on Thursday.

Tests confirmed they had the H5N1 virus, the Animal Health Department said.

The two provinces had reported outbreaks among ducks last month and are in the government"e;s watch list comprising 14 provinces and Can Tho city where bird flu has re-surfaced among poultry since early May.

On Saturday Vietnam reported its second human case of the virus in less tham a month, after a year and a half with no new human cases. Both victims were in hospital in stable condition, officials said.

A total of 42 Vietnamese have died since the virus re-surfaced in Asia in late 2003.

The Animal Health Department said 129 million poultry have been vaccinated against bird flu so far this year and 41 out of Vietnam"e;s 64 provinces and cities have completed the first phase of a vaccination campaign.

Agriculture Minister Cao Duc Phat has said the vaccination campaign should target all the country"e;s waterfowl flock.

Ducks and geese can carry the virus without showing they are sick, making it harder to detect the infection. The fowl spread the virus in their droppings as they roam from one rice field to another.

The virus has infected more than 300 people in 12 countries, 187 of whom have died, the World Health Organisation said.

Most human cases have involved people who have had contact with infected fowl. Experts fear if an easy means of transmission from human to human develops, there could be a pandemic affecting millions.