Arsonists are being blamed for causing most of the 105 fires in the Galicia region of northwest Spain, which borders Portugal. "There was fire everywhere", a resident of the town of Penacova told RTP television.
The 27 deaths, confirmed by Portugal's national civil protection agency, came four months after 64 people were killed and more than 250 injured on June 17, in the deadliest fire in the country's history.
"There are still places where security services have not yet managed to reach", civil protection agency spokeswoman Patricia Gaspar said, adding that the toll remained preliminary for that reason.
Authorities in both countries said that the strong winds from Hurricane Ophelia in the Atlantic Ocean and high temperatures fanned the fires, but investigations were also focusing on human causes.
Spain's Prime Minister, Mariano Rajoy, has travelled to the northwestern region of Galicia, where thousands of people have been evacuated.
The 524 registered outbreaks of fire in Portugal, by far the most since 2006, were caused by "higher than average temperatures for the season and the cumulative effect of drought", Gaspar said. Light rainfall was expected to help extinguish the flames.
Firefighters were battling 50 blazes in Portugal and a similar number in Spain on Tuesday (NZ time). Images broadcast on Spanish TV showed local residents, their mouths and noses covered with handkerchiefs, trying to contain the flames with buckets and pans of water. Most fires are set deliberately, officials say, and spread quickly due to poor forest management which leaves debris that fuels fires.
It is estimated that at least 5,000 hectares of land have been destroyed in Galicia and it has been reported on Monday that there are now 35 focal points in the neighboring region of Asturias.
Five wildfires were raging near Vigo, Galicia's biggest city, forcing authorities to close schools, roads and factories and shelter people forced to leave their homes in sports centres and hotels.
Regional President Alberto Nunez Feijoo called them "bordering on homicidal" and the Rural Environment Council also mentioned a "clear intent" behind the numerous blazes. The fire prompted the evacuation of hundreds of people. Two of the victims were found in a charred vehicle and the other one was an elderly man who died when trying to put out the flames in his house.
Alberto Nunez Feijoo, leader of Galicia, said Monday that numerous fires had started as acts of arson.