HANOI, May 20 (Xinhua) -- African swine fever (ASF) has spread to 34 cities and provinces across Vietnam, leading to the culling of 5 percent of the country's pig population, local media reported on Monday.

About 1.5 million pigs or 5 percent of Vietnam's pig herds nationwide have been culled since the first case of ASF was detected in the northern province of Hung Yen on Feb. 1, daily newspaper Vietnam News quoted Minister of Agriculture and Rural Development Nguyen Xuan Cuong as saying.

Without stronger preventive measures, "the most dangerous outbreak that the husbandry industry has faced so far" may spread to all 63 localities in Vietnam, he said.

The minister warned that even localities declared free from ASF, meaning there has not been an incident or suspected sick pig within 30 days, they are not entirely safe as the disease could easily return, as was the case in the central province of Thua Thien Hue.

At a working session in the rural district of Dong Anh in the capital city of Hanoi on Sunday, Vietnamese Prime Minister Nguyen Xuan Phuc called for joint efforts of the entire political system in the fight against ASF.

The prime minister underlined the responsibility of heads of concerned agencies in the combat and asked the agencies and localities to double efforts in ASF prevention and control. The veterinary sector needs to monitor and support pig farms that are free from the virus in pork consumption, he said, adding that localities should update agencies and people on developments of the disease.

ASF has hit pig farms in all 24 districts in Hanoi, killing 10 percent of its pigs. In Dong Anh alone, 629 pigs, or one-fifth of its total pigs, have been infected.

ASF is a severe viral disease affecting domestic and boars which can be spread by live or dead pigs and pork products, the World Organization for Animal Health said, noting that the ASF virus is harmless to human, but causes hemorrhagic fever in pigs and wild boars that is almost fatal.