Wildfires have flared across Portugal following a rise in temperatures and strong winds, ending days of cooler weather that had brought a brief respite from a spate of blazes, including one that killed 64 people in June.

The Civil Protection Agency said it was tackling 17 forest fires, deploying more than 1,500 firefighters and 24 water-dropping aircraft.

The number of wildfires ratcheted up from seven in the space of a few hours, with most afflicting areas in central and northern Portugal.

A stretch of Portugal's main north-south highway, the A1, was closed due to one blaze.

Massive clouds of smoke prevented the use of water-dropping planes in some places.

No injuries were reported.

Temperatures are forecast to keep rising in coming days, which could worsen what is already a bad year for forest fires.

Portugal usually has woodland blazes in the summer, but this year has been particularly unfavourable because around 80% of the country is experiencing "severe", or "extreme", drought conditions.

Wildfires in Portugal this year have accounted for more than one-third of the burnt forest in the entire 28-country European Union.

The EU's Emergency Management Service said almost 140,000 hectares (346,000 acres) of Portuguese woodland was charred up to August 5.

Across the EU, some 380,000 hectares (939,000 acres) have been burnt.

The agency said the area of blackened forest in Portugal up to August 5 is about five times larger than the average recorded in the country between 2008 and 2016.