At least 12 people died attempting to flee a wildfire in southern Spain, and 23 were missing, with firefighters on Friday still battling to bring one of the country's deadliest blazes on record under control.

The widely-circulated overnight total of 11 casualties was increased to 12 in a lunchtime update by the regional leader of Andalusia.

One Spaniard was among the victims and the rest appeared to be foreign nationals who ignored instructions to shelter in place, trying instead to flee by car as flames spread rapidly through a wooded area around the town of Los Gallardos in Almeria province, said Antonio Sanz, head of emergencies in the Andalusia region.

The area is a popular holiday destination and home to many foreigners, especially the French, Britons and Belgians.

Four people, who appeared to be British because the steering wheel of their car was on the right-hand side, died in one vehicle, he said.

Seven others were found dead after apparently abandoning their cars and attempting to escape on foot along a route that was not part of the evacuation plan.

"The consequences have been terrible. Everything seems to indicate that, in the case of the dead, the majority – or all of them – are foreign nationals," Sanz said.

The circumstances resemble those in neighboring Portugal in June 2017, when a huge wildfire during a heatwave killed more than 60 people and injured dozens more, with half of the victims burned to death in their cars as they tried to flee.

Early start to Spain's wildfires season

A series of early summer heatwaves has left large parts of Spain parched and vulnerable to any spark, triggering an early start to wildfire season.

So far this year, about 570 square kilometers have burned, about half the annual average for the past two decades and making up 40% of all the area burned in the European Union, according to the European Forest Fire Information System.

Last year, a record heatwave in August provoked the worst wildfire season in three decades, charring 3,300 square kilometers, an area twice the size of London.

"We usually don't see these fires until August. They're starting earlier now because the vegetation dries out sooner," Roman Garcia, a forest firefighter from Salamanca, said on state broadcaster TVE.

As authorities sought to identify the dead and track down the missing, anxious relatives from around the world posted messages on social media and local forums.

One woman said her daughter, who was driving a red Ford Fiesta and had her dog with her, was missing.

Another woman from the United States said her brother had been among a group of 10 people who tried to escape through a valley next to a stream. She shared the coordinates and asked emergency services to look for him.

Pedro Ridao, mayor of the nearby town of Antas, told TVE the fire was believed to have started when a power cable came loose and fell on a patch of dry scrubland on Thursday. 

However, a spokesperson for utility company Endesa ruled that out after technicians sent to inspect the cable found it carried no voltage.

"It was mainly the wind that was blowing in the afternoon that caused it to spread. As the afternoon wore on, we could see the fire was racing ahead, devouring farmhouses, holiday homes and cars, so we sprang into action," Ridao said.

Prime Minister Pedro Sanchez offered his condolences to the families of the victims and said he felt "enormous sadness and devastation".

The death toll makes it Spain's deadliest wildfire, surpassing a 2005 tragedy when a barbecue-sparked blaze in the central province of Guadalajara killed 11 firefighters.

That disaster prompted major changes to Spain's wildfire prevention and emergency response systems.