A forest fire in southern Spain is threatening a UNESCO World Heritage site famous for its biodiversity and endangered species.

At least 1,000 people were evacuated from the area where the fire started on Spain's southern coast, with the fire later advancing east to reach the Donana Nature Reserve, one of the country's most important wildlife sanctuaries.

The reserve protects more than 107,000 hectares considered of extreme ecological value for their mix of ecosystems, including wetlands, dunes and woods.

It is a key stop for migratory birds and home to a variety of animals, including about a fifth of the 400 remaining Iberian lynxes.

Photo: The Iberian lynx is extremely endangered, and the fire at Donana is within its territory. (Wikimedia Commons)

"The fire has entered in the limits of the reserve, and that is where we are focusing our efforts," said Jose Gregorio Fiscal Lopez from the regional Andalusian authority in charge of the environment.

Ecologists who work in the park are concerned the fire could wipe out some of the area's prized species and terrain.

"We are worried because the impact could be huge," Carlos Molina, an ornithologist who works inside the reserve, said.

"Donana is probably one of the most important areas for birds in all of Europe, and we just happen to be in a nesting season for several species," Mr Molina said.

While Mr Molina said the reserve's endangered Iberian imperial eagle should not be in danger, the area in immediate threat from the fire is territory for the extremely endangered lynx.

Blaze enters 'critical phase'

Photo: Officials are concerned about a possible change in wind direction. (AP: Alberto Diaz)

Juan Sanchez, director of Andalucia's forest fire prevention unit, said the fight was "in its critical phase" due to strong winds whipping up the flames.

"We are managing it, but a change in the direction of the wind could alter the situation," Mr Sanchez said.

Susana Diaz, the regional president of Andalusia, said no people have died in the blaze and "there's no risk to the population" after about 1,000 were evacuated from campsites and houses near the town of Moguer, where the fire started on Saturday night.

Ms Diaz said fighting the fire was proving difficult due to hot, dry weather, with temperatures reaching 39 degrees Celsius, and shifting winds.

Photo: Authorities are investigating how the fire started. (AP: Alberto Diaz)

Over 550 firefighters, soldiers and police officers supported by 21 air units were combating the blaze on Sunday.

"It's still very early, but we are not ruling out the human factor [as a cause of the fire]," Ms Diaz said.

Spain's interior minister, Juan Ignacio Zoido, said from a control post near the fire that since "we are taking special measures, even though the wind is pushing the fire toward [the reserve] to keep the damage to a minimum".

The fire comes a week after wildfires killed 64 people in neighbouring Portugal, which like Spain is suffering from a lack of rain and high temperatures.