Three planes, 27 fire engines and 120 Spanish firefighters have been helping to battle the blazes since Sunday, said a spokesman for Portugal's National Civil Protection Authority (ANPC).
By midday on Monday, six major fires were still burning, according to the ANPC website.
The heatwave gripping the centre of the country and the consequent dryness helped provoke the fires in the Santarem, Coimbra and Castelo Branco regions of central Portugal.
In all, 1,300 firefighters are fighting the blaze using some 400 fire engines and around 30 firefighting aircraft. As well as the Spanish help, Morocco sent Portugal one of its firefighting planes.
Spain's assistance came as part of the European Union's civil protection system that provides for mutual aid in emergency situations, said Christos Stylianides, the EU commissioner for civil protection.
It is the second time this summer that Portugal has had to call for European help. In June, a massive forest fire killed 64 people and injured more than 200 more near Pedrogao Grande in central Portugal.