Portugal's Civil Protection agency said the town of Góis, some 40 km from the forest fire's epicenter in the Pedrógão Grande region was now the most unsafe zone in the area affected by the fire, Efe news reported.
Spokesman Fausto Coutinho said: "it could have been a unusual coincidence, with a plane passing over and an explosion occurring on the ground at the same time".
Officials with the Portuguese government could not confirm the crash.
He said the fire had been started deliberately, and called for an investigation.
Although many Gibraltarians will have spent the long weekend in Portugal, most are likely to have stayed near the coast, far from the fires in the centre of the country. There have also been reports of propane tanks exploding in the fires.
But a spokesman for the civil protection agency said none of the planes fighting the deadly wildfires were missing.
Ouzenda residents were evacuated and firefighters moved in to protect the houses while aircraft battled the fire approaching the small village.
Jordan Lefort (Amiens) et Marvin Gakpa (Lorient) arrivent à Quevilly Rouen
Avec le FC Lorient, il a pris part à cinq rencontres de Ligue 1 (saison 2014-2015 et 2015-2016). Et n'avait pas rejoint les Merlus depuis, ce qui pouvait laisser présager un départ.
From early Wednesday, firefighting planes flew sorties over the smouldering forest canopy in the central Pedrogao Grande region, dropping water on the flames still licking pine and eucalyptus trees, according to an AFP journalist on the scene.
Spain, France and Italy have sent a total of 19 water bombers to help with the operation.
Since Saturday, more than 1,000 firefighters and more than a dozen water-dropping aircraft were deployed to tackle the blaze that had raged across the central region of Portugal, about 150 kilometers (95 miles) north of Lisbon.
Some firefighting resources were being diverted to Gois, about 20 kilometers from Pedrogao Grande, where nearly 800 firefighters and four planes were battling the flames.
Antena 1 public radio reporter Pedro Sa Guerra says there was thick smoke over the area on Tuesday caused by the devastating wildfire in Pedrogao Grande.
Of the 64 people who died, 47 of them perished on the N236 highway, 30 of them trapped in their cars as the flames surrounded them.
Costa's order asked three questions: whether extreme weather could explain the scale of the disaster, why emergency services communications at times didn't work, and why the road where the deaths occurred was not closed.
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