A Foreign Office travel warning has been issued after a “significant number” of forest fires broke out across central and northern Portugal.
Four people are reported to have died and more than 40 injured in blazes sweeping across the region.
More than 5,000 firefighters were struggling to bring 107 active fires under control on Tuesday, officials told The Times.
Of the 40 people injured, 33 were firefighters. The authorities said that the situation on the ground was “very difficult”.
Portuguese prime minister Luis Montenegro said the fires were “raging across the country”.
He thanked France, Greece, Italy and Spain for their “rapid and essential help in combating this scourge” in a post on X/Twitter.
The fires have burned homes and halted traffic on several motorways. The risk level varied from “very high” to “highest” depending on the region.
A series of blazes broke out over the weekend in the northern Aveiro region and forced about 70 residents to flee, according to the civil protection authority.
A forest fire in the area reached the outskirts of the town of Albergaria-a-Velha and burned several houses.
National civil protection commander Andre Fernandes was quoted as saying that the situation was likely to worsen amid unusually dry conditions and wind gusts of up to 43 mph.
He planned to maintain a special red alert status across mainland Portugal.
Updated Foreign Office travel advice said: “There are currently a significant number of forest fires burning in several parts of Portugal.
“The Portuguese government has declared a state of alert until 11:59pm on Thursday 19 September.
“Access to forests and activities in rural areas may be restricted. Roads may be closed due to smoke and ash.
The situation is fast-moving and could change rapidly. Keep up-to-date with developments and follow the advice of the Civil Protection Authority.”