European neighbors have responded to an urgent appeal for help from Portugal by sending aircraft used in water bombing forest fires.
“This is a very serious moment for Portugal,” said Mr Sampaio during a visit to the headquarters of the national fire service near Lisbon.
Portugal is enduring its worst drought since the 1940s.
About 3,200 fire-fighters backed by 800 vehicles and 30 aircraft are fighting the blazes with the help of hundreds of military and police.
The fires are being driven by 70-kilometer-an-hour winds and some were in rugged inaccessible terrain.
Several dozen people had to be evacuated from their homes in the Pampilhosa da Serra area.
Fire fighters said they heard “little explosions” which led them to suspect the fires may have been deliberately lit.
The situation was also critical at Abrantes, not far from Pampilhosa, where a number of houses were threatened by the fire.
Firefighters and local authorities suspect arson in the wave of fires which have so far killed 10 firefighters and burnt 134,500 hectares of forest and scrub land since the beginning of the year.
About 95 people have been arrested by police in Portugal this year and face arson charges.
Of the 18 districts in Portugal, 16 were on “maximum” or “very high” fire alert.
Mr Sampaio appealed to employers to release volunteer firemen from their work obligations “because at this time the country needs as many fire fighters as possible.”
Earlier, Prime Minister Jose Socrates acknowledged that the country was running out of resources to fight the fires and said he had invoked a European Union mechanism for cooperation in emergencies.
France and Spain were the first to respond to the appeal.
A Spanish plane was already in operation in the north of Portugal while a second plane was dispatched to Pampilhosa da Serra on Sunday.
Two aircraft have been sent by France while three heavy helicopters from Germany were to arrive today along with 25 firefighting experts.
Italy said it was immediately sending a Canadair aircraft and was weighing the possibility of sending a larger Beriev BE200 amphibious turbojet, which is capable of dropping 12,000 liters of water.
The plane was in operation against a fire in Sardinia, said a spokesman for the Italian civil defense, but could leave for Portugal on Monday.
The Portuguese were also calling on additional internal resources,
mobilising 2,000 members of the national gendarmerie force (GNR) to evacuate people, close highways threatened by fire and keep roads clear for fire trucks and ambulances.