Costa acknowledged that much more work was needed to prevent catastrophic fires, including diversifying the vegetation in Portugal's forests and establishing fire breaks.
High clouds of black smoke have towered for days over the Algarve region, a top European vacation destination.
While winds have made the firefighting effort more difficult, crew working overnight kept flames from reaching the town of Silves, a popular tourist spot and home to about 6,000 people.
The torrid weather that has hung over much of Europe for weeks also was subsiding, with a high of 31 C forecast for the Algarve on Wednesday.
Along with ground crews, 13 aircraft and more than 380 vehicles were battling the blaze.
In neighbouring Spain, 27 aircraft were helping some 700 firefighters put out a fire near Valencia. Radio broadcaster Cadena SER said nearly 2,900 hectares have been burned.