SAO PAULO, Brazil — A haze of toxic smoke clouds the tropical city of Porto Velho. Now patients are flooding its health centers.

During the first three weeks of August, the Cosme and Damião Children’s Hospital in Porto Velho admitted more than 400 children with respiratory problems — three times the average, according to officials. Brazil’s northwestern state of Acre reported 47,000 ­cases of respiratory illnesses during the same period. Lines at public health clinics are growing, and officials say they’re scrambling to hire more staff.

As fires spike across the Amazon rainforest, an environmental challenge is becoming a public health hazard.

“Every year we have some fires and issues with smoke, but this was the worst year of them all,” said Izaura de Campos, a pediatrician in Porto Velho. “This is the year when we are finally seeing what we are breathing.”

Children and the elderly are most susceptible to smoke-related illnesses, doctors say, but anyone who inhales the pollutants can be affected. The toxics can hinder breathing and oxygen flow and exacerbate chronic conditions such as asthma and bronchitis. Prolonged exposure can increase the risk of some cancers.

“Just one day’s exposure to these pollutants has a critical impact on health,” said Marcos Abdo Arbex, a pulmonologist in Sao Paulo state who specializes in environmental diseases. 

For those who live downwind of the flames, there’s no escape. Authorities in Porto Velho are telling residents to avoid exercise, stay inside and shut their windows.

Sarah Nachiro keeps her family inside and her windows closed. Still, she said, her 4-month-old son, Henrique, has suffered from coughing fits so strong he has turned purple. Weeks of colds and shortness of breath have left him on antibiotics. Sarah herself has been to the emergency room twice with asthma. She faults the government response for the effects on the country’s health.

“It’s a crime,” she said. “A complete lack of respect for the population as a whole but especially with the children.”

Campos said she has seen twice as many patients complaining of respiratory issues and colds as usual. The emergency room at her hospital is packed with children seeking oxygen, she said, and pharmacies have run out of saline solution.

Fires in the Amazon are common during the dry season, but this year has been exceptional. More than 25,000 fires have been spotted in the rainforest in August alone, a nine-year high, according to Brazil’s National Institute for Space Research.

The fires can burn for months on end, sending smoke hundreds of miles. Sao Paulo, the hemisphere’s largest city, was covered in a blanket so thick last week that it blocked out the midday sun, turning day to night.

In Porto Velho, some mornings Nachiro can’t see through the smoke in front of her house: “Everything is white.”

The fires, many of them set by farmers and loggers to clear land, are at the center of a growing international dispute between Brazilian President Jair Bolsonaro and other world leaders.

Bolsonaro campaigned for president last year on promises to open the rainforest to more development. The platform was popular in a country struggling through years of economic stagnation.

Since his inauguration in January, deforestation has surged. He has blocked new environmental protections and is accused of lax enforcement.

World leaders have described the Amazon as a global resource, a key defense against climate change. It accounts for a quarter of the carbon dioxide absorbed by the world’s forests.

Scientists warn that deforestation is approaching a tipping point — between 20 percent and 25 percent — when the degradation could become irreversible, and rainforest could become savanna.

French President Emmanuel Macron this week announced a $22 million package from the Group of Seven nations to help fight the fires. Bolsonaro, a climate change skeptic, questioned their intentions; his government so far has rejected the offer.

Bolsonaro has accepted help from Israel and Chile. President Trump has offered U.S. support.

Porto Velho’s state of Rondonia has been scorched by 4,600 fires this month. The government has sent 400 soldiers and dozens of firefighters to the region; military planes have showered water on the fires surrounding the city.

Campos, the pediatrician, said the government isn’t doing enough.

“It’s a massive level of negligence,” she said. “We don’t see any effective measures to put a stop to it. People need to be more conscious of the impact this has on the children.”

With little rain forecast in the coming weeks, the fires show no sign of abating. Activists have called for a ban on Brazilian beef and leather products to protest Bolsonaro’s policies.

In a meeting with Bolsonaro on Tuesday, Amazon state governors on Tuesday called for federal help fighting the fires. But they also stressed that environmental protection should not get in the way of economic development.

“We can’t protect our rivers and forests in poverty,” said Helder Zahluth Barbalho, governor of Para state. “As long as our people are hungry, we can’t conserve.”

Arbex, the pulmonologist, warned that environmental de­gradation also has a cost. 

“You cannot put a price tag on the suffering that individuals will experience,” he said. “But there is also a rise in costs for people and the government.

“If there is a huge increase in emergency room visits and hospitalizations, serving that population will be more costly.”