Firefighters were finishing extinguishing the Kingaroy bacon factory fire late on Sunday afternoon, as a scientific team tried to determine whether the smoke from the blaze contained toxic chemicals.

A Queensland Fire and Emergency Service (QFES) spokesperson said crews were dampening down hot spots at 4pm.

The building itself was still standing but had suffered significant damage after being engulfed in flames about 7.45am.

QFES scientists were taking air samples to work out whether toxic smoke had risen from the blaze, after an exclusion zone of at least a kilometre was established as a precaution.

Nearby residents were being urged to keep windows and doors closed while motorists should avoid the area.

A total of 10 fire crews remained on site on Sunday afternoon and there had been no reported injuries.