More than 450 firefighters backed by helicopters and planes were deployed across a hilly 30-kilometre (19-mile) front in the northeastern province of Tarragona, the Catalonia region's fire service said.

The blaze had devoured an estimated 3,137 hectares (7,751 acres), with the protected Els Ports natural park representing about one-third of the total, according to Catalan rangers.

An AFP journalist at the scene saw a helicopter swoop over burning vegetation and a house to drop water as grey smoke billowed from the green hills.

The blaze had gutted an isolated hillside home, which stood surrounded by scorched trees, its roof collapsed.

Firefighters said they were "cautiously optimistic" as they worked to stabilise the blaze and prevent it spreading further into the park.

"The changing wind patterns in the area will determine the fire's progression," the service added in a statement.

The emergency response could "begin a stabilisation phase in the final hours of the day", said the leader of Catalonia's regional authority, Salvador Illa.

Catalonia's civil protection authority urged residents to shut their doors and windows and stay home, saying around 18,000 people were affected.

Overnight gusts of up to 90 kilometres (56 miles) per hour had thwarted efforts to extinguish the fire, prompting reinforcements from the Spanish army's emergencies unit.

Scientists say human-induced climate change is increasing the intensity, length and frequency of the extreme heat that fuels forest fires.

Spain has in recent days sweltered through a heatwave that parched the land and heightened the risk of forest fires.

National weather agency AEMET said last month was Spain's hottest June on record and that the frequency of extreme heat had tripled in the past 10 years.

According to the European Forest Fire Information System, around 500 fires destroyed 300,000 hectares in Spain in 2022, a record for the continent.

Around 21,000 hectares have burned so far this year.