The disease, which is fatal to pigs but harmless in humans, has spread to every province on the Chinese mainland since its initial detection in August 2018.

Authorities previously said they hoped the disease would not spread to Hainan, an island located off China's southern coast.

Among 517 pigs across the six farms, 146 had died of the disease, according to a notice posted on Sunday (21 April) by China's Ministry of Agriculture and Rural Affairs.

The local government has begun control measures including quarantine blockades and culling programmes, it said.

China is the world's biggest producer and consumer of pork, and the rapid spread of African swine fever has raised concern of a potential shortage.

Pork output fell 5.2 percent in the first quarter of 2019 compared with a year earlier, showed official statistics released last week.