A spate of wildfires have put firefighters under "tremendous pressure," prompting calls for people to put out barbecues and cigarettes properly.
North Wales Fire and Rescue Service still had crews at six wildfires on Tuesday evening after dealing with multiple blazes in the past 24 hours.
Fires have also broken out across Wales over the past week.
Officials have described the number of incidents as "unprecedented".
Kevin Roberts, senior fire safety manager at North Wales Fire and Rescue Service, said: "These fires place tremendous pressure on our resources.
"In these dry conditions, fires involving grass, bracken and heather can develop extremely quickly, especially in raised winds, and fires can soon get out of control.
"So if you are out, it is more important than ever in these conditions to make sure that any smoking materials are discarded and extinguished properly.
"If you are out camping, again make sure that campfires or barbeques are fully extinguished. Better still, avoid open fires altogether in this dry period."
North Wales fire crews have been called to 44 small fires and six large fires in the open since midnight on Monday and were still tackling the following blazes on Tuesday evening:
- Mynydd Cilgwyn, Carmel, near Caernarfon
- Braichmelyn, near Bethesda
- Pentre Halkyn, Holywell
- Bangor Mountain
In Gwynedd, 15 homes were evacuated on Monday evening as crews fought a mile-long mountain fire at Mynydd Cilgwyn in Carmel, near Caernarfon.
Overnight and 20 miles away, residents in Braichmelyn, near Bethesda, were on standby to leave their homes when a fire broke out in a nearby pine forest at about 03:10 BST.
Both blazes are under control, along with another fire at Bangor mountain, and the areas are continuing to be monitored.
Our thanks go out to our firefighters who are working hard in challenging & arduous conditions to combat wildfires in the region – and we’re also grateful to the employers of our retained staff who have released them from work to assist us with incidents #proud #thanks— North Wales Fire (@NorthWalesFire) July 3, 2018
Robert Williams of Natural Resources Wales said trenches would be dug around Braichmelyn and filled with water to stop any further fire spreading.
He added: "We've never had fires like this for a number of years. This is quite unprecedented for ourselves."
A number of other fires have broken out across Wales in the past few days.
A large fire at Maerdy mountain in Rhondda Cynon Taff on Friday reignited on Tuesday morning.
Ferndale Community School, which is nearby, opened on Tuesday - but staff were advised to keep all doors and windows closed and not go out at lunchtime because of the smoke and ash.
South Wales Fire and Rescue Service said the blaze had been extinguished, but crews would continue to monitor and check the area.
Pembrey Mountain in Carmarthenshire was another location to see a fire from previous days reignite.
On Monday, crews also tackled blazes at Kilvey Hill in Swansea, and Penrhys, Rhondda Cynon Taff, while there was also a large forest fire near the Bryn Pica landfill site in Aberdare.
What causes wildfires?
- Hot, dry weather and wind all make the perfect recipe for a wildfire
- Sometimes fires start naturally, ignited by heat from the sun or a lightning strike
- The majority are the result of arson, campfires, discarding lit cigarettes, barbecues, not burning debris properly, or playing with matches or fireworks
Across the weekend, a helicopter was brought in to drop water on the Cwm Rheidol mountainside and a fire was tackled at Garth Hill in Maesteg, Bridgend county.
Andy Fry, chief fire advisor for Wales, said wildfires were fairly common, but there had been twice as many as an average June.
He added: "Historically there have been a number of years where we've seen very significant numbers of wildfires, particularly in 2015.
"Things are not going to get any wetter in Wales for the foreseeable future. The drier things get, the more risk there is that a fire will start."