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The two girls, aged 13 and 14, were crushed by falling trees while sleeping in a tent.
Around 20 other children were injured when the storm hit the campground for Boy Scouts and Girl Guides hosting 140 youngsters in the northern village of Suszek.
It took hours for firefighters to clear away trees and other debris from access roads before they could reach and evacuate the scouts from the camp pitched in a forest flattened by violent wind.
“We were really scared and we just stayed put until all the trees came down,” a boy scout who was not named told the TVN24 news channel.
Aerial television footage showed trees in vast swathes of forest snapped like matchsticks by raging winds that meteorologists said were hurricane-force.
Elsewhere a woman died when a tree fell on her house in the northern village of Konarzyny, while a man sleeping in a tent in a nearby village also perished after being hit by tree brought down by high winds.
Authorities in the same region also confirmed the death of a fifth victim, a 48-year-old man, crushed by a tree.
Thirty-seven people were reported injured nationwide while power was intially cut to around half a million homes and businesses as violent winds downed trees and ripped off roofs in northern, western and southern regions.
Winds even blew off part of a reinforced concrete roof from a multi-family block of flats in the central city of Gniezno, TVN24 reported.
Poland’s Prime Minister Beata Szydlo promised financial aid for the hardest hit municipalities after meeting with a crisis unit coordinating the emergency response from the Baltic port city of Gdansk.
An unusual heatwave saw peak temperatures soar to more than 30 degrees Celsius (around 100 Farenheit) across Poland in recent days, but milder weather is expected this weekend when the mercury is forecast to dip to the mid-20s in most regions.
More hot weather and storms are however forecast for eastern regions on Poland’s border with Belarus.
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