Agriculture officials on Tuesday said African swine fever has been found among pigs at a farm in Yuen Long.

The Agriculture, Fisheries and Conservation Department (AFCD) said the outbreak does not pose a risk to food safety and the virus will not infect humans.

The department said tests on samples taken from 32 pigs at the farm in Lau Fau Shan found half to be infected with the virus, adding that it has ordered that all the pigs be culled on site.

The AFCD said other pig farmers in the area were notified of the outbreak and the department's staff have inspected three other farms within a three-kilometre radius.

"No abnormalities were found in the health of those pigs. For the sake of prudence, the AFCD has also temporarily suspended movements of pigs on these farms and will take samples from pigs for testing to ensure there is no infection on the farms," a spokesman said in a statement.

"No reports of abnormalities from pig farms outside the three-km zone have been received."

Dirk Pfeiffer, a specialist in animal infectious diseases at City University, said the outbreak will not affect the operation of local slaughterhouses, or the overall supply of live pigs.

"We do get a lot of pigs coming in from the mainland so I don't think we will actually have a significant impact on the pork even though that particular farmer has quite a large number of pigs," he said.

"I think it will probably be fairly ineffectual in terms of the pork price. Maybe there will be a little bit of fluctuation, but I'm pretty sure that they can compensate fairly quickly by increasing numbers from the mainland."