HANOI, Vietnam — Asian nations are scrambling to contain the spread of the highly contagious African swine fever, with Vietnam culling 2.5 million pigs and China reporting more than a million dead in an unprecedentedly huge epidemic that some governments fear has gotten out of control.

Smaller outbreaks have been reported in Hong Kong, Taiwan, North Korea, Cambodia and Mongolia after cases were first reported in China’s northeast last August. The UN Food and Agriculture Organization is expected to release a weekly update Thursday on the scale of infections, which could show the numbers rising significantly.

With supply dwindling as No. 1 pork producer China and hard-hit Vietnam destroy huge numbers of herds and tighten controls on shipments, prices have soared by up to 40% and caused shortages in other markets.