China reported its fourth outbreak of African swine fever on Thursday, bringing the total number of pigs killed by the disease to more than 500 since the start of this month.

The outbreak was reported on Friday in Yueqing, Zhejiang province, where pigs raised by three households died for unknown reasons, according to a statement from the Ministry of Agriculture and Rural Affairs.

The disease was confirmed as African swine fever on Wednesday. Some 430 pigs had been infected as of Thursday morning, with 340 deaths, the ministry said.

Local authorities have taken quarantine and sterilization measures to control the disease, and the outbreak has been contained, it said.

China reported its first ever African swine fever outbreak on Aug 1, in the northeastern city of Shenyang, Liaoning province, where 47 pigs died after becoming infected.

Investigations are underway to determine the source of the disease, according to the ministry, which said the disease is deadly to pigs but does not transmit to humans.

China is the world’s biggest producer and consumer of pork.