At about 2pm, crews were alerted to a grass fire near Breadalane. The fire swept through five hectares of grassland before crews were able to contain it. The southbound lane of the Hume Highway was closed.

Then at about 3pm, crews were alerted to a separate fire on the Hume Highway near Collector. By 4pm, both incidents had been contained.

The cause of those fires is undetermined.

"We have concerns someone might have discarded a cigarette out of a car window," Southern Tablelands RFS operational officer, Lachlan Gilchrist said.

Police are continuing investigations.

The latest forecast showed temperatures in Crookwell will climb to a maximum of 36 degrees later in the week. However, the RFS is more concerned with conditions leading into the weekend.

Vegetation will have a low moisture content because of high winds impacting the area, Mr Gilchrist said.

"Its certainly gearing up for a very difficult summer."

A severe fire danger rating is in place in the Southern Tablelands area for November 19. For updates visit: rfs.nsw.gov.au