SIMFEROPOL - Thousands of people in a Crimean town have been evacuated after a leak at a chemical plant, authorities said on Thursday.

Nearly four thousand mostly children have been relocated from Armyansk in the north of Moscow-annexed Crimean peninsula, and surrounding villages this week, the regional education ministry said.

The Ukrainian border service on Thursday shut down two checkpoints on the de-facto border close to the town due to the “dangerous ecological situation”, while Ukrainian President called the situation an “environmental catastrophe”.

Residents have been complaining for two weeks of sore throats and acrid smells, saying metal surfaces became rusty and oily on the night of Aug 23 and trees in the town lost their leaves. No official reaction followed however until their grievances culminated in a protest on Tuesday, leading authorities to launch a probe into a leak of sulphur dioxide and shut down the town’s main factory Crimean Titan, a producer of titanium dioxide.

Titanium oxide is a white powder widely used in various industries including paint, cosmetics and food. Sulphur dioxide is a waste product of the manufacturing process.

Crimea governor Sergei Aksyonov on Thursday ordered medical workers to go door-to-door and take blood samples from residents closest to the factory’s acid waste storage reservoir, which is believed to be the epicentre of the leak.

Water levels in the acid waste reservoir have dropped, evaporating harmful chemicals, the Crimean government said.

Crimea’s emergency ministry chief Alexei Yeremeyev said his workers were constantly spraying trees and roads with water and handing out face masks.

Poroshenko said in a statement on national television that a special international commission must find the reason behind the “environmental catastrophe” in Armyansk, adding that “sources” suspect it to be Russian military drills in the area.

Ukraine border service spokesman Oleg Slobodyan said that two out of three crossings between Crimea and mainland Ukraine will be shut down, though they would still process Ukrainian citizens “trying to flee the disaster.”

Crimea’s governor Aksyonov denied that there was any threat of pollution spreading from Armyansk.

However AFP’s correspondent in Crimea’s main city Simferopol, some 130 kilometres south of Armyansk, reported receiving official text message warnings advising recipients to “avoid travelling around the city”, wear a gauze mask in case of strong smells and wash exposed skin with water if acid rain causes any blisters.

Crimean Titan, a significant titanium dioxide producer in the European region, has suffered greatly from the peninsula’s isolation after its annexation by Moscow.

Sanctions caused it to lose its western export markets while a transportation blockade by Ukraine has undermined supply of raw materials.

Aksyonov on Thursday blamed Kiev for causing the accident and “causing a panic with social networking bots”.

“Everybody knows that the main reason behind the situation in Armyansk is the blockade of the water supply by Ukraine, which in itself is an act of terror,” he wrote on Facebook.

“Authorities have never lied to you,” he said. “React only to information from official sources.”