Authorities warned "complicated" conditions as they battled fires in the coastal tourist region of Valparaiso amid an intense summer heat wave, with temperatures soaring to 40 degrees Celsius (104 degrees Fahrenheit) over the weekend.

Rosana Avendano, a 63-year-old kitchen assistant, was away from home when the fire began to sweep through the city of Vina del Mar, where she lives with her husband.

"It was terrible because I couldn't get (to my house). The fire came here... we lost everything," Avendano told AFP.

"My husband was lying down and began to feel the heat of the fire coming and he ran away."

She feared the worst for hours, but eventually was able to contact her spouse.

"We can sadly confirm that there are 64 deaths," Boric said from Quilpue, outside the hard-hit city of Vina del Mar.

"The figure is going to rise. We know it is going to increase in a significant way," he added, saying it was the country's deadliest disaster since a 2010 earthquake and tsunami that killed 500 people.

- Death toll could rise -

Boric has declared a state of emergency, pledging government support to help people get back on their feet after he flew over the affected area in a helicopter Saturday afternoon.

According to the national disaster service, SENAPRED, nearly 26,000 hectares (64,000) acres had been burned across the central and southern regions by Sunday.

SENAPRED chief Alvaro Hormazabal said firefighters were battling 34 blazes as of Sunday morning, with 43 others under control.

Weather "conditions are going to continue to be complicated," Hormazabal said.

Authorities imposed had a curfew beginning at 9:00 pm Saturday (0000 GMT Sunday), while thousands in the affected areas were ordered to evacuate their homes.

In the hillsides around Vina del Mar, AFP reporters saw entire blocks of houses that were burned out overnight Friday into Saturday.

Some of the dead were seen lying on the road, covered by sheets.

- 'Inferno' -

The fires, blazing for days, forced authorities on Friday to close the road linking the Valparaiso region to the capital Santiago, about 1.5 hours away, as a huge mushroom cloud of smoke impaired visibility.

Images posted online from trapped motorists showed mountains in flames at the end of the famous "Route 68" leading to the Pacific coast.

According to Interior Minister Carolina Toha, the weekend blazes have been "without a doubt" the deadliest fire event in Chile's history.

"This was an inferno," Rodrigo Pulgar, from the town of El Olivar, told AFP. "I tried to help my neighbor... my house was starting to burn behind us. It was raining ash."

The fires are being driven by a summer heatwave and drought affecting the southern part of South America caused by the El Nino weather phenomenon, as scientists warn that a warming planet has increased the risk of natural disasters such as intense heat and fires.

The rising temperatures threaten to engulf more of South America, as brigades in Argentina have been fighting a fire that has consumed more than 3,000 hectares in Los Alerces National Park, famed for its beauty and biodiversity, since January 25.