Kakanui Volunteer Fire Brigade Chief Fire Officer Brent Dungey said fire crews managed to save two neighbouring buildings, but the shed was too far gone by the time fire crews arrived at 11.05am.
"It is a shame about the old cars, but no-one was hurt and the other two buildings were all right," Mr Dungey said.
One of the neighbouring buildings was only 1m from the blaze, he said.
Fire crews from Kakanui, Weston and Oamaru attended, including three tankers and three other fire appliances. The crews controlled the fire and left the scene about 2pm.
Although the cause was unknown, it was unlikely there would be a need for an investigation, a Fire and Emergency New Zealand spokesman said.
The owner was supported by neighbours on the side of the road watching fire crews work.
