Fresh horse flu outbreak at four NSW properties

The New South Wales Department of Primary Industries (DPI) has started a horse flu vaccination program north of Wollongong after an outbreak of the virus at Darkes Forest and Helensburgh.

Four properties at Darkes Forest and three at Helensburg, south of Sydney, have been infected and placed under quarantine.

The zoning of the area has been changed from amber to red.

The department's deputy chief veterinary officer, Ian Roth, says the area has been zoned for vaccination but no horses have been immunised yet.

Mr Roth says the new zoning will allow the department to move in and start vaccinations quickly to stop the virus spreading further.

"It'll be north of Wollongong and than we'll move," he said.

"We'll vaccinate north and that way, the immunity starts about seven to 10 days after vaccination and so you start south just in case there is a little bit more southerly spread."