A fault on a Newcastle- bound freight train set off a series of fires between Gunning and Goulburn on Sunday night.

Rural Fire Service duty officer Mick Uren said the first of 12 outbreaks was reported at 7.50pm. Thirty-five crew members from Gunning, Parkesbourne, Goulburn Mulwaree Support, Oolong, Cullerin and Middle Arm brigades responded.

Mr Uren said the train sparked a fire at Oolong, south of Goulburn, and burnt out about 500 metres beside the railway line. About 2km of country was burnt between Breadlabane and Yarra but there were also other smaller fires, including around Parkesbourne and near the 'Cardross' property.

They were mostly contained to the rail corridor and "benign" in nature except where sparks set off stacked sleepers in one section, he said.

"Access was the biggest headache. We couldn't always get near the rail line," Mr Uren said.

Long grass beside the line also posed challenges. Cardross owner Guy Milson said the fire burnt 2.5km along his boundary fence but did not affect his land.

"It didn't really escape so we were very lucky," he said.

"We were saved by the Rural Fire Service's wonderful work. They were fantastic and gave up their Sunday night to do that."

Mr Milson said he noticed the line of fire on his boundary at about 7.55pm. The fact that he had sowed crops next to it stopped its spread.

Crews worked until 2am to fully douse the outbreaks.

One bogie of the train derailed close to Joppa Junction, some 7km from Goulburn.

It's understood a fault on the train's bogie caused the fires.

An Australian Rail Track Corporation spokesman said a crane and replacement bogie arrived on site on Monday morning and crews undertook recovery work. Train services were delayed as a result. Operations resumed at 6pm that night.

"Track damage has occurred and repairs will be required, but the extent of these will be subject to further assessment once the wagon has been removed," he said on Monday.

"...The incident has been reported to the Independent Australian Transport Safety Bureau and will be investigated by ARTC."

By Tuesday, all services were operating but a temporary speed restriction was in place for this section of track to allow what ARTC described as "minor, final re-sleepering and repairs to take place between train services.

Asked about the long grass beside the track, the spokesman said ARTC undertook a "significant amount" of rail maintenance annually, including vegetation clearance. 

"(ARTC) is committed to keeping the rail corridor and rail operations safe," he said in a statement.

"If community members wish to raise a vegetation concern with ARTC, they can contact ARTC’s Enviroline on enviroline@artc.com.au or 1300 550 402.  

Meantime, a NSW Trainlink spokesperson said on Monday the recovery work delayed services on the Sydney to Melbourne line due to speed restrictions.

However trains were able to run through the fire affected area on Sunday night at reduced speed.

Sunday 9pm

The Rural Fire Service is dousing a series of spot fires along the rail corridor south of Goulburn.

RFS duty officer Mick Uren said about 12 fires had broken out, the first one at 7.50pm on Sunday night. They are believed to be between Gunning and just south of Goulburn, around Parkesbourne and Yarra.

Mr Uren said they were started by a train, which has since pulled up. The rail corridor has been closed to allow crews to extinguish the outbreaks.

The fires are largely being contained within the rail corridor and no property is under threat. Low fuel and benign conditions are assisting firefighters.

Crews from Mulwaree Support, Gunning, Parkesbourne, Cullerin and Middle Arm are among those attending.

No other details are available at this stage.