Doctors in a Russian town treated dozens of children complaining of dizziness and nausea on Wednesday because of noxious fumes coming from a local dump, authorities said.
Residents of Volokolamsk, some 120 kilometres (75 miles) west of the Russian capital, have long complained about high levels of hydrogen sulphide and nitric oxide from the Yadrovo landfill.
Riot police were called in this month to disperse a protest calling for the closure of the site.
Doctors treated 50 children from different schools in the town, the regional authorities said in a statement, adding that the main complaints were nausea and dizziness.
Andrei Vorobyov, the governor of the Moscow region, said plans were in place to send the affected children out of the area.
"The situation is getting worse and worse with each passing day... because of the gases coming from the landfill," town mayor Pyotr Lazarev told Business FM radio.
Around 200 people had gathered outside the Volokolamsk hospital Wednesday, an AFP journalist said.
One person was holding a sign reading: "We are suffocating! We so want to live, you know."
"Don't kill our kids," another placard read.
Anna Luzova, 10, said she had worn a medical mask to school on Wednesday because the smell outside was so strong.
"It smelled like something had exploded. I almost couldn't breathe. Sometimes, almost every night, we wake up from that smell. What will it be like in summer? I don't know how we can live like this," she told AFP.
"It's been impossible to breathe here for two months. Our children are suffering from nausea and hypertension," Anna Grapeh, a 50-year-old resident said.
Governor Vorobyov visited the landfill site in the afternoon, his press service said.
He then arrived at the Volokolamsk hospital, where residents shouted "Shame!" and threw snowballs at him, an AFP journalist saw.
Three buses of riot police were also at the scene.
"This is unfortunately not the first story of its kind. This is a very complicated situation," Vorobyov said.
He added that a new facility would be built which would not emit gases.
The Yadrovo landfill should be covered with earth within the next few days, authorities said.
The ministry for emergency situations said the landfill was the source of "pollution in the air" in Volokolamsk and the surrounding area.
But following an air quality test, it said "no threat to residents of the town had been detected".
On social media, several people complained of an unpleasant smell in the town and said their children were forced to leave school earlier than usual because they felt ill.