The incurable pig disease was detected at a farm in the outlying District 9, HCMC Department of Agriculture and Rural Development announced Tuesday.

Nguyen Phuoc Trung, the department’s director, said the farm's owner fed the pigs with leftover food at restaurants, suggesting that could be a cause of the infection.

More than 160 pigs at this farm have been culled and the outbreak is under control, officials said.

District 9 borders Dong Nai, the country's largest pig-farming province which was infected by African swine fever last month.

With HCMC hit by African swine fever, the total number of infected cities and provinces in Vietnam has now jumped to 55 out of 63, including the other four major cities, Hanoi, Hai Phong, Can Tho and Da Nang.

By Tuesday, Vietnam had culled 2.45 million infected pigs. African swine fever virus is shed in blood, saliva, tears, nasal secretions, urine, faeces, and secretions from the animal's genital tract. Pigs can therefore become infected by contact with many different infected sources, mainly infected pigs, pork, and other pig-derived products like swill and fomites like bedding, according to the Food and Agriculture Organization.

African swine fever, which has no cure but does not affect humans, first came to Vietnam in early February and quickly spread across the northern and central regions before reaching the south in early May.

With the country estimated to lose VND3.6 trillion ($154 million) from the disease so far, Prime Minister Nguyen Xuan Phuc had called for severe penalties for anyone trying to subvert efforts to contain it, saying that "fighting African swine fever is like fighting invaders."

Vietnam has the seventh largest number of pigs in the world, 30 million, and is the sixth largest pork producer. Pig farming provides a livelihood to 2.4 million households, according to official figures.

Pork makes up 70 percent of the average Vietnamese diet. The Ministry of Industry and Trade is looking at frozen pork supplies as a fail-safe plan for a possible pork shortage. The Ministry of Agriculture and Rural Development has warned people not to continue raising pigs, and to raise other animal groups like buffalos, cows, poultry or seafood instead.

Latest data collected by June 6 from the World Organization for Animal Health shows 13 countries and territories are suffering from new or ongoing outbreaks of the disease: Belgium, Hungary, Latvia, Moldova, Poland, Romania, Russia, Ukraine, mainland China, Hong Kong, North Korea, Vietnam and South Africa.