Firefighters have already been called to four deliberate blazes at a frequently-targeted Aberdeen hill this year.
The sky above the Gramps, at Kincorth, was lit orange once again on Friday night with billowing smoke visible from some distance.
The nature reserve has long been plagued by firebugs, with crews called there dozens of times over the summer months in recent years.
Police have since launched an investigation into the latest blaze, which was first reported to emergency services at around 6.10pm.
Officers, fire investigators and local politicians have now made a desperate plea for information – warning that the fire-raising must be stopped before someone is hurt or widespread damage is caused.
Last night fire chiefs said there had been four confirmed deliberate fires since January 1 and warned the blazes were “dangerous and unacceptable”.
The service’s senior officer in Aberdeen, Bruce Farquharson, said: “When firefighters respond to deal with these unnecessary incidents it means they aren’t available to respond to genuine emergencies.
“Every deliberate fire has victims, costs – and consequences.
“Deliberate fires put firefighters and members of the public at risk and can damage large areas of land and endanger wildlife.
“We will continue to take a zero tolerance approach to these incidents, working closely with our partners at Police Scotland in an effort to trace anyone involved in this unacceptable and criminal behaviour.”
Local politicians urged anyone with information about who was starting the fires to come forward before someone gets hurt.
Kincorth councillor Alex Nicoll said: “This is incredibly concerning news and I would encourage people to think of the potential consequences of their actions.
“Ultimately, by deliberately starting a fire you could be putting someone’s life at risk by tying up resources.”
Fellow Kincorth representative Sarah Duncan expressed disappointment that firefighters and residents were again being put at risk.
“It’s worrying that people have such little thought for others,” she said.
“Excellent work has been done in schools and the local community in recent years to educate residents about the dangers of wildfires and I hope this will continue.
“I’d urge anyone who knows who may be setting these fires to contact Crimestoppers so these incidents can be stopped before someone gets hurt and widespread damage is caused.”
Sgt Eoin Maxwell, from Nigg Community Policing Team, said: “I’d appeal for anyone with any information on the cause of the fire, or who saw anything suspicious in the area, to please come forward.”
Anyone with information should call the police on 101, or the Crimestoppers charity on 0800 555 111 if they would prefer to remain anonymous.
