United Kingdom — North Wales Fire and Rescue Service were originally called to Llandderfel near Bala just before 21:00 BST on Sunday.
The fire was initially dealt with but a spokesperson said it had reignited on Monday morning.
Elsewhere crews attended gorse fires in Chwilog near Pwllheli, Gwynedd and Llanfairfechan, Conwy.
Crews from Bala, Llangollen and Dolgellau were first called to the incident at Llandderfel on Sunday evening and tackled the fire until the early hours of Monday.
Relief crews from Corwen then took over before crews from Bala, Dolgellau and Llangollen returned with crews from Ruthin and Blaenau Ffestiniog.
An environmental protection unit from Wrexham is also at the site.
The gorse fire in the grounds of a holiday park in Chwilog, Pwllheli ignited five times between 14:00 BST on Sunday and 08:29 BST on Monday with the original blaze thought to have been started deliberately.
In Conwy, the gorse fire was reported at 09:25 BST on Monday in Pool Street, Llanfairfechan.
Bob Mason from the North Wales Fire and Rescue Service said: “Fires like this place tremendous pressure on resources, with firefighters tied up for a considerable length of time trying to bring them under control.
“These fires can also place lives and homes at risk, blight the countryside and waste large amounts money.”
In the current conditions with “tinder dry” land the fires can spread very quickly, Mr Mason added.
“As yet we do not know whether the fire in Llandderfel was started deliberately or accidentally.
“We are urging visitors to the countryside to take extra care when they are out and about and reduce the risk of fire,” he added.