The incident occurred early Wednesday morning in the Fornebu district just outside the Norwegian capital, NRK reports.
Traditional celebrations (russefeiring in Norwegian) by Norwegian upper secondary school (gymnasium) pupils in their final spring semester usually start on around April 20th and end on May 17th, Norway's national day.
Students commonly wear coloured overalls and hire buses, cars or vans in which they travel around local towns. The young school leavers often celebrate continually during the month-long period.
One person received light injuries in Wednesday morning's fire, according to reports.
Police were alerted to a blaze on one of the buses just before 7am on Wednesday, according to NRK.
On arrival at the scene, emergency responders found the fire to have spread to two similar vehicles.
Up to 15-20 other vehicles at the garage are reported to have also been damaged by smoke and heat.
Nobody was on board the bus when the fire started, NRK reports.
The fire was extinguished by 9am.
“For a while there was some risk of [the fire] spreading to the building, but given fire services now have control of the fire, there is no longer a risk,” Oslo Police response leader Torgeir Brenden told NRK.
Police wrote on Twitter that around 60 people had been evacuated from the area and that one person had sustained light injuries from inhaling smoke. The affected individual was treated at the scene.
Brannen er slukket. ca 60 personer ble evakuert. 1 person lettere røykskadet. Vi undersøker nå åstedet for å finne årsaken til brannen.— OPS Politiet Oslo (@oslopolitiops) May 2, 2018
Police also tweeted that they were investigating the scene in an effort to determine the cause of the fire.
The manager of one of the the russ buses bemoaned the incident.
“This has ruined half of the russ period,” said, Marte Classon, manager of the ‘Soft City' bus, one of the three vehicles destroyed by the fire. Classon was speaking to newspaper VG.
“It is completely burned down, from top to toe,” Classon said.
Classon and 12 other people have spent months working on the bus in preparation for the student festival season. Although the group never sleeps on the bus, many valuables had been left inside it.
The bus was covered by insurance, according to VG's report.