The Fire Service and Horizons Regional Council are continuing to monitor a compost fire on Hinau St and say smoke will be visible in the area while it is put out.

Firefighters were called to the smoldering compost heap after it spontaneously ignited just before 7am yesterday morning.

Whanganui Fire Station officer Jes Sorenson said it started due to a combination of the compost pile being very dry and Tuesday night's rain.

"It is spontaneous ignition," Mr Sorenson said. "The compost, when it is breaking down, it heats up."


He said the moisture would have accelerated the process.

"There was a lot of smoke in the area."

Mr Sorenson said it started in the centre of a three to four metre pile of compost and the fire had to be dug out.

"It's just a matter of clearing it out," he said.

"It's not something you can put out immediately. It's not a major, it's just a bit of a time consuming thing."