Authorities have stepped up efforts to trace up to 200 horses exposed to equine influenza (EI) in rural New South Wales as the number of horses confirmed infected with the virus has surged to more than 25.

NSW Minister for Primary Industries Ian Macdonald has confirmed more horses have been stricken with EI at Parkes, Tamworth, the Windsor area north-west of Sydney, Wyong on the Central Coast and Berry.

Mr Macdonald also confirmed the number of cases at Sydney's Centennial Park had nearly doubled from 11 reported cases yesterday to now stand at 20.

The number of cases detected at the government's quarantine facility at Eastern Creek, in Sydney's west, remains at five.

"Further testing overnight and this morning has confirmed that there are a number of cases of equine influenza in other parts of the state,'' Mr Macdonald told reporters in Sydney.

"These test results have come up positive and indicate that there has been some spread of this disease beyond the Sydney region.''

More than 150 departmental staff are trying to find up to 200 horses that were at a Carol's Ranch Riding Club Event at Maitland, in the Hunter Valley, last weekend, which three infected horses from Centennial Park attended.

"Suffice to say we have to locate all the horses that have been in contact with horses from Centennial Park and eliminate any other potential source of infection,'' Mr Macdonald said.

"That's why it's very important that people who have attended the Carol's Ranch Event last weekend get in contact with us and have those horses tested.''

The minister would not speculate on how much longer the nationwide ban on all horse racing events, imposed yesterday, would remain in effect.
But he said it would remain in place "for longer than 72 hours''.

"At the moment, the repercussions are quite severe because of the postponement of racing events,'' he said.

"If we can ensure that horse owners keep their horses to their current paddocks and on their properties and report any signs of illness, we have a chance of getting a hold of this before it slips across from the show circuit and gymkhana circuit into the thoroughbred industry.''

.A 72-hour nationwide lockdown - ordered by federal Agriculture Minister Peter McGauran - remains in place, preventing horses, ponies, donkeys, mules and zebras from being moved.