The fire began on a hectare of land containing a pine plantation at the corner of Millett Road and the Calder Freeway about 7.20am.

Gisborne fire brigade Captain Tony Wade said it took about 50 firefighters two hours to control the blaze.

"Just because of the heavily forested area," Capt. Wade said.

The property loss from the fire was minimal, with some pine trees and fences burnt, but the main concern was fire damage to the base of a power pole.

Capt. Wade said the pole was attached to powerlines that supply Gisborne and run all the way to Woodend.

Fire operations had to cease while the power pole was secured.

It was being replaced yesterday afternoon.

The cause of the fire was not known, and CFA investigators deemed it suspicious, said Sergeant Will Watkins, of Gisborne police.

Gisborne detectives are investigating the matter.

Anyone with any information should contact Gisborne police station on 5428 2500 or Crime Stoppers on 1800 333 000.

Police are also investigating arson attacks at the Gisborne Primary School.

Senior-Constable Stephen Muscat, from Woodend police, said offenders attempted to set fire to a portable classroom about 3pm on Wednesday.

He said the arsonists pierced holes in aerosol deodorant cans and put them in a bin, pushed the bin against the portable and set it alight.

A week earlier, offenders gathered the same sort of aerosol cans on an outdoor table, surrounded them with bark chips, and set the bark alight, Sen-Constable Muscat said.

Police urge anyone with any information to come forward.

Those with information should contact Crime Stoppers on 1800 333 000, or Woodend police on 5427 2610.

Meanwhile, fire destroyed a $100,000 house south of Kerang this week.

Senior-Sergeant Greg Deveson said the fire took hold of the house in Kelly Road, Tragowel, between 7pm and 9pm on Wednesday.

The occupants of the house were not present when the fire occurred, Sen-Sgt Deveson said, and the cause of the fire was unknown at this stage, but was not suspicious.