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.