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Firefighters are currently heading to another fire near the scene of five deliberately lit fires early this morning.

The latest fire is in a pocket of bush on Old Mountain Rd about 10k from Te Pahu Rd.

A helicopter has arrived at the scene and firefighters are liaising with Department of Conservation staff.

The fire is approximately 100m by 60m in size.

This morning's fires west of Hamilton threatened to flare in the tinder dry conditions and burn through Department of Conservation land and a nearby farm.

Instead, the five fires tied up volunteer and professional fire fighters from 4.35am when the initial call came in, until after daybreak.

Police are now investigating the incident, that sparked along the isolated stretch of Old Mountain Rd southwest of Whatawhata.

Te Awamutu Sub-Area Manager, Senior Sergeant Dave Simes said a local man woke to see a fire several kilometres up the road.

"Driving to investigate the man confirmed the light was from a fire and called 111."

Mr Simes said arriving firefighters noticed five separate fires at various intervals along the left side of Old Mountain Rd, all within 6km of the intersection with Te Pahu Rd.

"The first fire was about 2.75km from Te Pahu Rd and engulfed about 500m of scrub along the roadside and destroyed 200metres of fencing belonging to one farm property. The second blaze was 2km further along the road and burnt about 42m of long grass on the roadside.

"About 540m further on was a third fire that ran from the side of the road up a steep embankment. It had burnt under the greener foliage and reached the drier scrub further up.

Firefighters had to climb the steep embankment to reach the effected areas and spent several hours extinguishing the various hotspots and cutting down several trees to prevent further outbreaks."

Mr Simes said a smaller fourth fire was lit a short distance away and was located between the third and fifth fires, the last blaze being the largest fire about 60m away from the third.

This fifth fire also ran up a large embankment creating further challenges for those fighting the fires.

Eight fire appliances from Pirongia, Te Awamutu, Ngaruawahia, Morrinsville and Hamilton attended.

Fire investigator Peter Hallet said the first staff on the scene were confronted with a blazing stretch of gorse and scrub running about 500 metres long and 20 metres deep beside the road.

As they worked to get it under control the Pirongia crew drove further up the road and discovered two more fires.

Mr Hallett found the fourth.

''It appears to us they've been deliberately lit. There's no other credible reason for them to start,'' he said.

Lightning and power lines were ruled out as possible causes, yet evidence was scarce.

The likelihood of someone having four smokes within 10km was also low, Mr Hallet said.

That leaves the ''credible'' scenario of arson.

''Given the potential for these fires to be deliberately started you'd have to wonder at the mindset of the people that do this at the best of times,'' Mr Hallett said. ''Let alone when the whole country's tinder dry''.

- © Fairfax NZ News