The news comes as firefighters tackle two major fires in the Greater Manchester area – one at Saddleworth Moor and one at Winter Hill, which is around 50km (30m) away.
Soldiers from the Royal Regiment of Scotland arrived to help firefighters with the blaze at Saddleworth Moor on Thursday.
The area affected by the third fire is within the Otterburn training area in Northumberland, the country’s second-largest firing range.
The blazes are 15km apart and started on Sunday, according to reports.
If the area affected spreads beyond the training area, which is Ministry of Defence land, then the fire service will be called in.
For now, military personnel have been sent to Otterburn and the fires will be allowed to burn themselves out, due to the risk of unexploded ordnance in the area.
An army spokesperson said We can confirm there are fires at two locations on the Otterburn Training Area following live firing exercises.
There is currently no risk to people or property but we will continue to monitor the situation carefully.
The local fire brigade has been informed.
News Source SkyNews