Six crews were called to an industrial estate on St Asaph Avenue, Kinmel Bay, at about 17:45 BST on Tuesday.
North Wales Fire and Rescue Service said the fire was now under control.
A spokesman added: "Crews will remain at the scene for some time tackling any hotspots and damping down".
The road remains closed at Denbigh Circle, Clwyd Park and St Asaph Avenue until further notice.
A North Wales Police spokesman said they were likely to be closed until Wednesday morning.
Crews from Rhyl, Prestatyn, Colwyn Bay and Abergele were sent to tackle the blaze.
People have been allowed to return to their homes after being evacuated due to a large fire at a commercial garage in Conwy county.