Fire crews are responding to a fire at the rugby grounds on Bethlehem Road.

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

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

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

A SunLive photographer at the scene says it was the toilet block that has nearly burnt to the ground and the roof has collapsed in.

Colin says a fire investigator and police have been called to the scene as well.

The cause of the fire is yet to be established.

At the scene? Call 0800 SUNLIVE.