Some 2,500 people were evacuated from areas near the blaze, which is sweeping through a wooded, mountainous area in La Palma, one of the lesser-known, unspoiled islands of the Spanish archipelago off the coast of Africa.
A park ranger died while fighting a blaze in the Canary Islands allegedly sparked by a German man who set fire to toilet paper after defecating in the woods.
Firefighters continued to battle the flames on Friday morning with the blaze showed no sign of abating and has already ravaged an estimated 3,000 hectares of ancient woodland.
"The fire has not come under control yet," Fernando Clavijo, regional president of the Canaries, told reporters on Thursday night.
"The situation may get more complicated throughout the night. It's not going to be easy."
The giant smoke plume was visible in NASA satellite images.
Imagen satélite Aqua Modis Nasa, todo Archipiélago, impresiona humo W de la Palma pic.twitter.com/6qLgMvJcTD— Meteo RTVC (@MeteoRTVC) August 4, 2016
The ranger, Francisco Jose Santana, died while working to put out the flames, said Spain's UGT union of which the 54-year-old was a member. "He leaves a wife and five children," it added.
The Guardia Civil said they arrested a 27-year-old German man on Wednesday afternoon, suspected of having caused the fire.
The man, whose identity has not been revealed, "told officers he accidentally provoked the blaze when he defecated... and set fire to the toilet paper he used for that," the Guardia Civil added in a statement.
The man has been accused of causing a forest fire through negligence, and was expected to be questioned by a judge Thursday, it said.
Some 200 people are fighting the blaze, as are helicopters and planes, a spokeswoman for the Canary Islands' emergency services said.
Weather conditions are not making their task any easier, as high temperatures and strong winds fan the flames, she added.
Acting Prime Minister Mariano Rajoy sent his condolences to the park ranger's bereaved family.
Mi más sentido pésame a la familia del fallecido en el incendio de La Palma y mi apoyo a tantas personas como trabajan en su extinción. MR— Mariano Rajoy Brey (@marianorajoy) August 4, 2016