Hot temperatures and a bit of moisture are believed to have sparked a twenty metre high fire in Christchurch's Selwyn district.

Fire crews were called to a forestry site off State Highway 73 between Springfield and Sheffield, just before six this morning.

They arrived to find a blaze making its way through a pile of debris spanning around 100 metres in length.

Principal Rural Fire Officer Douglas Marshall said the fire is now contained.

"The forestry crew who's onsite have been pulling apart the heap and moving the material that needs to be moved out and dampened it down."