The Department of Conservation believes a campfire may have caused a bushfire in Fiordland.

The fire last night burnt through about a hectare of bush at Doubtful Island in Lake Te Anau.

It was safely extinguished by five DOC staff after about four hours.

Another ground crew then worked to dampen it down.

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DOC said there are strong indications the fire was caused by a campfire that wasn't properly extinguished.

Incident controller Ross Kerr said people think the forest is wet, but it's not.

He said a total fire ban is in place and a fire ban means no fires at all.

Meanwhile, spontaneous combustion is the likely cause of a hay stack fire in Canterbury.

Rural fire-fighters were called to a Swannanoa property north of Christchurch at about six last night.

Senior station officer Tristan Roberts said engines from Kaiapoi, Pines beach and Brooklands took more than an hour to bring it under control.

He said the fire is not suspicious.

"The probably cause is spontaneous combustion which is where high-moisture hay stacks can have a chemical reaction that builds heat,'' he said.

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"Hay basically insulates so the larger the hay stack, the less cooling effect there is to offset the heat.''

Mr Roberts said farmers are giving into the temptation to bail hay when it is a bit too damp and this is one of the risks.

He urged farmers to check the temperature of their stacks.