Children get a dose of oxygen from a Red Cross volunteer at a village in Jambi.

Indonesian forest fires are putting nearly 10 million children at risk from air pollution, the United Nations warned Tuesday, as scientists said the blazes were releasing vast amounts of greenhouse gases.

The fires have been spewing toxic haze over Southeast Asia in recent weeks, closing schools and airports, with people rushing to buy face masks and seek medical treatment for respiratory ailments.

Jakarta has deployed tens of thousands of personnel and water-bombing aircraft to tackle the slash-and-burn blazes set to clear agricultural land. The fires are an annual problem but this year are the worst since 2015 due to dry weather.

An elderly villager gets a dose of oxygen from a Red Cross volunteer outside his home in Jambi.

Almost 10 million people under 18 -- about a quarter below five -- live in the areas worst affected by fires on Indonesia's Sumatra island and the country's part of Borneo island, the UN children's agency UNICEF said.

Small children are especially vulnerable due to undeveloped immune systems while babies born to mothers exposed to pollution during pregnancy may have low birth weights and be delivered early, they said.

"Poor air quality is a severe and growing challenge for Indonesia," said Debora Comini from UNICEF.

The blazes have been spewing toxic haze across Southeast Asia, forcing the closure of schools and airports.

"Every year, millions of children are breathing toxic air that threatens their health and causes them to miss school -- resulting in lifelong physical and cognitive damage."

Thousands of schools have been closed across Indonesia due to poor air quality, with millions of youngsters missing classes.

Schools were forced to shut across Malaysia last week as dense smog from its neighbour clouded the skies, while Singapore was also shrouded in haze during the weekend's Formula One motor race.

Agence France-Presse