Following a crisis meeting of President Luiz Inacio Lula da Silva's cabinet, Environment Minister Marina Silva announced a "war against the fire" and said federal police were investigating the "atypical situation" that has caused extensive damage and disruption.

Tarcisio de Freitas, the Sao Paulo governor, decreed a state of emergency in 45 municipalities and said two people suspected of starting fires had been arrested.

With dense smoke drifting across a wide swath of Brazil -- even reaching capital city Brasilia 720 kilometers (450 miles) to the north -- several flights have been canceled and travel on some roads has been halted.

"I stuck my nose out last night around 7:00 pm and I had a lot of trouble breathing," 66-year-old retiree Carlos Rodrigues told AFP. "I've lived here 32 years and I've never seen anything like it."

Two factory workers died Friday in Urupes, in the northern part of the state, while fighting a fire, officials said.

The military aircraft being deployed include a KC-390 Embraer, a converted troop transport craft that can drop up to 12,000 liters (3,170 gallons) of water on fire zones.

The Embraer was sent to one of the cities most threatened, Ribeirao Preto, about 300 kilometers from Sao Paulo.

But Lula said the plane "was unable to operate because of the amount of smoke," adding: "That gives you an idea of the problem."

Videos posted on social media showed the city plunged into near-darkness by a dense layer of smoke. Some residents have had to evacuate.

"It's apocalyptic," a person is heard saying on one video.

Around the region, farm fields have burned and scores of cattle have died.

Governor de Freitas said 10 million reais (around $1.8 million) was being allocated to help farmers who lose crops or livestock.

Amid prolonged drought, Sao Paulo state is experiencing its worst month for fires in decades, with 3,480 separate blazes identified, according to INPE, the National Institute for Space Research.