Fire crews were called to a layby near Victoria Services on Sunday following reports of a trailer with a wheel on fire.
When a crew from St Dennis was sent to investigate they confirmed that the fire had spread to the trailer and was well alight.
A land rover from St Dennis was also mobilised to the scene where firefighters were using two hose reel jets and two breathing apparatus to tackle the blaze.
Police were also requested to attend the scene as smoke was affecting the traffic on the A30.
Two further appliances from St Columb and Newquay were mobilised to the scene for water. Firefighters used crash rescue equipment to cut access to the trailer, approximately 6000 litres of water was used to extinguish the fire.
At 17:15 on Sunday afternoon it was confirmed that the A30 had been reopened.
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