Fire authorities are concerned about the smoke and police have been requested to ask all employees in shops from The Square to Church Street (both sides of the street) to leave until further notice.

Hazmat officers are securing gas readings in the area and monitoring the atmosphere.

They have underpinned the evacuation decision.

Duty Commander with the NSW Fire and Rescue Service, Tom Freedom (Dubbo) said it is not certain how long the evacuation order will be in place, but every effort will be made to return shop traders as soon as possible.

The control of the fire scene however, is expected to continue for quite some time.

Commander Freedom said the cause of the blaze was not yet known and that police - with assistance from fire personnel - would determine the cause and origin of the blaze.

It is also believed that other buildings at the rear and adjacent to the Auslec buildings were not penetrated by the fire, but structural damage has occurred.

Commander Freedom said the destroyed building contained electrical gear and merchandise which becomes toxic when on fire.

The resulting smoke from the blaze spread throughout the main area of Parkes.