Canary Islands regional president Fernando Clavijo said police suspected arson and had opened three lines of investigation. There are no reports on any arrests.
More than 12,000 people have had to evacuate their homes since the blaze broke out on Wednesday.
Hundreds of soldiers and firefighters have been deployed to get the flames under control, and improved weather conditions helped them make more progress yesterday.
Governor Rosa Davila said after a “very difficult night”, emergency services had enjoyed some “positive results”.
Many locals are sheltering in sports halls, clubs, and pavilions and no injuries have been reported.
People are being urged to stay inside due to the poor air quality.
Meanwhile, Spain’s mainland is expected to endure heatwave temperatures for the next several days, with temperatures topping 40C (104F) on Wednesday and Thursday.
Although the blaze in the northeast of the island is not near the main tourist areas in the southwest, the regional government ordered the evacuation of a state-run hotel in the Teide volcano national park, in central Tenerife, some 30 miles southwest of the fire zone.
Dávila said that more than 12,000 people have been evacuated from their homes.
The islands’ emergency services said Sunday that 11,600 hectares (29,000 acres) of pine forest and scrubland had been burned.
The fire, described as the worst in Tenerife in decades, is threatening 11 town areas flanking a steep and craggy mountain area. Access for firefighters is extremely difficult.
More than 400 firefighters and soldiers have been deployed, as well as 23 water-carrying helicopters and planes.
On Tenerife, the agency predicted maximum temperatures averaging 30 C (86F) for the coming week.
