A fire the Bethlehem Sports Ground that destroyed a shed was not deliberately lit.

Police spoke to two youths in relation to the fire and determined it was not deliberately lit, a police spokesperson says.

The fire occurred around 6pm on Thursday.

Fire and Emergency New Zealand northern fire communications shift manager Colin Underdown says the fire was completely alight when the fire crews arrived.

'It was well involved on arrival and it's a single story sports ground building, 10m by 5m.”

He says two low pressure units and two crews did an offensive exterior attack.

Colin says a fire investigator and police were called to the scene.