" Summercourt fire destroys 35 Western Greyhound fleet buses "
The blaze - the cause is not yet known - is expected to cause "significant disruption" to services in mid-Cornwall, including school buses.
Mark Howarth from Western Greyhound said: "A lot of hard work has gone into Western Greyhound and it's awful to see it going up in smoke."
The burnt-out buses included two brand new vehicles which cost more than £100,000 each, and four of Truro's six park-and-ride buses.
One bus was damaged but is "repairable".
Significant disruption Mr Howarth, the company's managing director, told BBC Radio Cornwall: "I could just see flames leaping in the air and, when I arrived, all the buses at the bottom of the yard were completely ablaze.
"The services will be significantly disrupted but we will run as much of them as we can."
He added: "There will be work for the drivers tomorrow."
Incident Commander Guy Herrington, from Cornwall Fire and Rescue Service, said: "Because of the flammable liquids and materials in the buses, the fire took hold very quickly.
"It takes very little for fire to spread from one vehicle to another but to tackle this number of vehicles in one go is rare."
The fire service said more than 60 firefighters tackled the blaze, and strong winds "significantly fanned the flames".
Neighbour Kelly Broderick said the winds meant "you couldn't tell which way it was going to go".
She said: "It was big, there were explosions; it was terrifying, to be honest."
Water from a swimming pool at a nearby house was used by fire crews fighting the blaze.
In Cornwall about a third of services are not operating or have been delayed, although services are running normally in Devon.
Western Greyhound has been operating buses in both counties since 1998.
It describes itself as a "locally based, family-run business".
There was no damage to the depot's offices or workshops and there were no reports of any injuries.
The cause of the fire is being jointly investigated by Devon and Cornwall Police and Cornwall Fire and Rescue Service.
Investigators said they were keeping an "open mind" as to how it started.