The horse, in the north-west of the state, has been described by state agriculture officials as "highly suspect for equine influenza".
An initial test returned a positive result. A second test is understood to have returned negative.
The results of further testing should be known around midday Australian Eastern Standard Time today, or mid-afternoon in New Zealand.
Tasmanian re-instated its ban on horse movements at 5.30pm yesterday.
"This means that all horses throughout Tasmania must remain on their current properties until further notice," a Tasmanian Department of Primary Industries spokesman said. "This will be reviewed as the latest lab test results become available."
No horses have been allowed into Tasmania since the outbreak began on mainland Australia.
The recreational horse in question has been placed in isolation. It is understood to have competed on the Tasmanian show circuit.
In New South Wales, more than 2500 vaccinations have so far been administered in buffer zones across the state. The first round has been completed in the Mittagong and Gloucester buffer zones.
Vaccinations in the Barmedman, Dubbo, Wellington and Armidale buffer zones are near completion and are continuing in the Forbes, Parkes and Mudgee buffer zones.
"We are going to beat this disease," a spokesman said. "The policy is still to contain and eradicate equine influenza as quickly as possible.
"There have been a few escapes into the green zone which is disappointing. We have responded to contain the new outbreak. Although there are people who think that the task is impossible, many experts are surprised that we have been able to contain it all."
This was due in no small part to the cooperation of the horse community, he said.
There are currently 4121 infected properties in the state, with 401 considered "dangerous contact" and 464 official "suspect".
"The number of infected properties being reported daily in Tamworth, the Hunter Valley and the Sydney basin are all showing promising signs of decline. This has resulted in a levelling of the overall numbers of infected properties across the state."
State authorities have moved to expand the purple zone.
Primary Industries Minister Ian Macdonald announced the expansion of the purple zone to incorporate Camden, Maitland and Tamworth.
"This common-sense decision frees up movements for thousands more horse owners and breeders in the heavily infected expanded purple zone," he said.
"Expanding the zone will greatly reduce the economic impact this contagious disease is having on our horse industries and allow the multi-million dollar horse breeding industry to resume.
"It means activities such as show jumping, dressage, pony carnivals, and three-day events can go ahead - as long as the horses are fit and healthy and stay within the purple zone.
"It also means drought-affected horse owners, who were previously forced to buy in feed for their horses, will now have the opportunity to agist them elsewhere in the purple zone."
Under the new zoning arrangement, the purple zone will stretch from Tamworth to Camden, linking known highly infected areas in between. The purple zone includes all or part of Penrith, Liverpool, Camden, Wollondilly, The Hawkesbury, Gosford, Wyong, Newcastle, Lake Macquarie, Port Stephens Great Lakes, Cessnock, Maitland, Dungog, Singleton, Upper Hunter, Muswellbrook, Tamworth, and Liverpool Plains.
"The purple zone still represents an area of high infection where lateral transfer between properties is happening at a substantial rate," Mr Macdonald said. "Horses can move into the purple zone with a permit but cannot leave until authorised."
In Queensland, the number of infected properties stood at 947 yesterday, an increase of 19 from the day before. New infected properties were at the Ipswich racetrack, Mount Nebo (about 30km west of Brisbane), Preston and Greenmount.
A number of horses at Rockhamption have been tested for the disease, after showing flu-like symptom. Results are expected today.