This was the scene fire fighters were faced with as they battled "mile-long" grass fires.
Dramatic footage captured the extent of the flames at both Maerdy and Rhigos mountains in Rhondda Cynon Taf yesterday.
Images show flames "licking the sky" as more than 88 hectares of mountainside were ablaze - following fires in Brenmenyn, Gilfach Goch and Treharris.
Residents compared the scene as like something from the apocalypse.
One Twitter user said: "Sad to see the Rhigos mountain ablaze tonight & Mountain Ash too! Poor wildlife. So many vulnerable lambs this time of year too."
Another added: "Rhigos/Treherbert mountain literally looks like a scene from an apocalypse film at the minute."
Abercynon councillor Elaine George added: "Myself and Councillor Lewis and liaising with police and fire authorities and keeping up to date with any information.
"We just hope the the people responsible will understand the consequences of their actions."
A spokeswoman for South Wales Fire and Rescue Service confirmed that the initial 999 calls came in at around 3.20pm - before fire crews spent hours getting the fire under control.
On Monday night the South Wales Community Mountain Rangers shared pictures of heavy smoke on Maerdy Mountain.
The group, which supplies water and food to emergency services, said: "This is only a section of the mountain! Take your time if you drive over Maerdy Mountain, fire and smoke everywhere. Just done a drop off before we move to our next location, so many fires today."
On Sunday emergency services were called out to a large grass fire on the Gower.
Last month residents were evacuated as a precaution after a blaze caused a "one mile fire front" at a Welsh beauty spot in Bettws-Y-Coed.
Fire chiefs said investigations into the cause of the fires were underway.
