Minister Waldez Goes said that four planes will be mobilized initially "to fight the flames and monitor affected zones."

They include a KC-390 Embraer, a troop transport craft converted to be able to drop loads of up to 12,000 liters of water on fire zones.

Among the cities most threatened is Ribeirao Preto, with a population of more than 700,000, about 185 miles (300 kilometers) from Sao Paulo.

Residents of one upscale neighborhood there have already had to leave their homes, the G1 news site reported.

Videos posted on social media showed Ribeirao Preto plunged into near-darkness Saturday by a dense layer of smoke.

"It's apocalyptic. Lots of wind, lots of smoke -- you can't even see the city. And it is 5:00 pm," a person wearing a protective mask is heard saying on one video.

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

Late Saturday, Sao Paulo Governor Tarcisio de Freitas declared a state of emergency in 45 towns and cities and announced that 10 million reais (around $1.8 million) was being allocated to help farmers who lose crops to the flames.

Some 40 cattle on one farm died in a fire, town officials in Santo Antonio do Aracangua said.

Locals are hoping that rain, expected to reach much of the area in coming hours, will help douse the fires. Prolonged drought in the region has aggravated the situation.

Sao Paulo state is experiencing its worst month for fires since data were first kept in 1998, with 3,480 separate blazes identified, according to the National Institute for Space Research (INPE). That's more than twice the number tallied last year.