The fires spread rapidly into the weekend through parched fields at the peak of the country's dry season in a region that has not had rain for months. Clouds of smoke cloaked nearby cities where outdoor activities were restricted, and highways and airport operations disrupted due to low visibility.

"We had an explosive combination of three factors: high temperature, very strong winds and very low relative humidity in the last few days. So, anything could cause an ignition," Sao Paulo Governor Tarcisio de Freitas said at a press conference.

He said three suspects were arrested in the region with containers of gasoline to start fires and a fourth man was arrested on Monday when he was caught setting fire to grass. Federal police are investigating the fires for suspected arson. Dry weather has increased the frequency of wildfires across Brazil this year, including in the Amazon region. Environmental experts said higher temperatures brought by climate change and widespread deforestation have contributed to the doubling of the number of fires this season. -- Reuters