The red alert, the highest on the scale, will take effect between 00:00 on Wednesday and 23:59 on Sunday, announced Duarte Costa, commander of ANEPC.
The 13 districts covered by the red alert are Aveiro, Braga, Bragança, Castelo Branco, Santarém, Coimbra, Guarda, Portalegre, Porto, Vila Real, Viana do Castelo, Viseu and Leiria.
ANEPC decided to keep an orange alert, the second highest on the scale, for Beja and Faro, which was already in force for these districts, and raise from yellow to orange the alert for Lisbon, Évora and Setúbal, between Wednesday and Sunday.
ANEPC stressed the importance that everyone keep aware of the risk of forest fires, remembering that "there are only fires if there is an ignition first".
11,492 field operatives, 60 firefighting planes and helicopters and a reconnaissance helicopter are available for the job.
Nuno Moreira, of the Portuguese Institute of the Sea and Atmosphere (IPMA), warned that the next few days will have very high temperatures, which could reach 40ºC in the southern regions and the Tagus Valley and be higher than 30ºC in the rest of the country.
Very hot nights are also expected in Lisbon and the Tagus Valley, never dropping below 20ºC and very low relative humidity values, particularly on the coast, which is unusual.
A strong wind is still expected, especially in the mountainous regions and in the centre and north of the country.