Waikato Firefighters are back on the ground near Meremere today - taking on a blaze that's burned through more than 520 hectares of swamplands

The 11-kilometre perimeter fire, covers the Whangamarino wetlands, a Department of Conservation area of environmental significance.

Eight helicopters, two planes and 40 personnel battled the fire yesterday, that broke out Monday afternoon - and is still not contained.

Incident Commander Mark Tinworth says crews are trying their best to preserve as much of the land as they can.

He says fire investigators have also been on site and the cause of the fire has yet to be confirmed.