Firefighters have been tackling a blaze involving about 100 tonnes of waste in Launceston.
Cornwall Fire and Rescue Service said seven crews were called to an industrial premises at Pennygillam Way at about 20:00 BST on Wednesday.
Crews have been making good progress damping down, said the fire service.
Firefighters were also called to a fire that spread across four flats in Trevose Road, Truro, at about 01:30 BST. There were no reports of injuries.
At the Pennygillam blaze, firefighters said a large amount of smoke was produced by the fire, but favourable winds meant the town was not badly affected by it.
Incident commander Mike Tremellen, from Cornwall Fire and Rescue Service, said: "The smoke was being produced in the early and mid stages of tackling the fire itself.
"Fortunately for us the wind direction proved very favourable, in that it wasn't going over the town itself, so it wasn't affecting residential areas as such."
In Launceston, Cornwall Council tweeted the household waste and recycling centre was temporarily closed due to the nearby blaze.