A fire that has scorched more than 17,000 hectares of bush continues to advance on a town in southwestern NSW.

The Cobbler Road fire was 18km west of Yass on Wednesday morning but advanced to within 11km of the town by the afternoon.

More than 120 firefighters battled the blaze with the assistance of 51 trucks and 10 aircraft, but haven't been able to bring it under control.

The fire may threaten properties in Black Range Road and the Ferndale, Sunnyside, Spring Vale, Wattle Valley, Yowerweema, Katandee and Euralia areas later on Wednesday.

A rural property in Glenroy Road may also be affected.

Yass and the township of Bowning are not under threat, but smoke is visible from Yass.

Rural Fire Service deputy commissioner Rob Rogers says bulldozers are being used to set containment lines and backburning will be done if necessary.

"It certainly has the potential to cause quite significant devastation if it were to continue along its current path," Mr Rogers told reporters.

"But I'm confident we will protect the township of Yass."

Yass Mayor Rowena Abbey said unofficial estimates suggested about 21,000 animals had been lost in the blaze so far.

Some properties have been damaged but it remains unclear how many, with many landholders and farmers only just starting to assess the damage.

"With 17,000 hectares burned, sheds and all sorts of things will have gone," Ms Abbey told AAP.

An evacuation centre has been set up in Yass, but most landholders have chosen to stay to defend their properties.

Ms Abbey, whose own property was in the path of the fire at one stage on Tuesday before the wind changed, said the mood among Yass residents was cautiously optimistic.

Jane Southwell, director of a farm near Bowning, said the blaze was a few kilometres from her land.

"We've got helicopters dropping water at the moment because it's inaccessible country and they really do have to get on top of it," she told AAP.

Remote properties in Bibinda Road and Childowla Road have come under threat and the 330kV Yass-Tumut electricity transmission line could also be threatened as the fire advances.