At least 32 people, including a one-month infant, have died in a spate of late-season wildfires ravaging parts of Portugal, according to officials.

In neighbouring Spain, the weekend blazes also killed at least four people and prompted the evacuation of thousands in the northwest region of Galicia, as the remnants of winds from Hurricane Ophelia fanned the flames along Iberia's Atlantic coast.

Firefighters on Monday were still battling 50 fires in Portugal and a similar number in Spain. Officials in the two countries said arsonists had started some of the blazes.

The late-season fires returned to Portugal four months after a summer blaze claimed 64 lives in one night. This year's current total of 96 deaths makes 2017 by far the deadliest on record for forest blazes in the country.

The wildfires, made worse by a prolonged drought combined with unusual high mid-October heat, tore through the parched forests of central and northern Portugal.

Portugal's central districts of Coimbra and Castelo Branco, as well as Viseu further north, were worst hit by the fires.

The government asked for international help and declared a state of emergency in territory north of the Tagus River - about half of its landmass.

"We are facing new (weather) conditions ... In an era of climate change, such disasters are becoming reality all over the world," Constanca Urbano de Sousa, Portuguese interior minister, said, citing the fires burning in the US state of California.

Authorities called on residents to fight the flames themselves, as firefighters could not be expected to reach all affected areas. Countless streets were no longer passable, while water-spraying planes could not be deployed to most fires due to gigantic plumes of smoke affecting visibility.

The weekend's fires had also injured 56 people in Portugal, civil protection service spokeswoman Patricia Gaspar said. The toll could still increase as seven people were unaccounted for.

But she said rains expected late on Monday and on Tuesday in the north of the country were likely to bring some relief.

The Portuguese government has been criticised for a slow, inefficient response and a lack of fire-prevention policies in a country with the largest woodland areas burned by wildfires in Europe.

Portugal's fires burned over 40 percent of the total in all of the European Union this year. With just 2.1 percent of the EU's landmass, Portugal was its biggest burner during 2008-16 as well, with an average of 36 percent of the total.

At the heart of the issue lie age-old traditions in the management of the land, made up mostly of small plots that have become fire hazards after they were abandoned by new generations of landholders who moved to the cities.