Police in south-central Chile have arrested a man on suspicion of starting one of the recent wildfires that killed 20 people and razed entire neighbourhoods, the government said on Wednesday.

Security Minister Luis Cordero said the suspect used a liquid accelerant to start fires in a wheat field, with authorities seizing five litres of fuel from him.

He was arrested at dawn in the town of Perquenco in the Araucania region, south of Biobio.

The fires began simultaneously on Saturday in various parts of the Biobio and Nuble regions, about 500 kilometres south of the capital Santiago.

Fanned by strong winds and high temperatures, the flames quickly ripped through the coastal towns of Penco, Lirquen and Punta de Parra, leaving a blackened landscape of smouldering ruins.

Around 1,000 homes went up in smoke, affecting around 7,500 people.

Other fires were later reported further inland, in the Biobio town of Florida, about 40 kilometres east of the city of Concepcion and in Araucania.

Cordero said substances used to start fires, including plastic containers containing accelerant, were found in Concepcion.

Firefighters were still battling 35 blazes on Wednesday – 22 in Biobio, five in Nuble and eight in Araucania, according to national forestry officials.

A drop in temperature in recent days has helped ease the situation.

"We managed to reduce the intensity of the fire," said Carlos Zulieta, a firefighter in Florida, adding that it was now advancing "more slowly."

The government said it would pay compensation of US$700 to US$1,500 to victims.

Aid began trickling into affected areas on Wednesday.

Municipal workers and private companies were delivering portable toilets and generators to Lirquen, where some families are camped out in the ruins of their homes. (AFP)