The fierce hailstorm has battered parts of Slovenia, Croatia and Germany since Monday as strong gale-force winds brought cold temperatures along with intense rainfall.
Enormous hailstones were found in Stari trg ob Kolpi, Deskova vas and Predgrad, Slovenia by Marko Korosec, who is a weather adviser for traffic and highways.
The 37-year-old said: "There was significant damage to cars and houses, complete destruction in some areas.
BRUTAL severe hailstorm with hailstones up to ~12 cm across (close to 5") in Predgrad, soth Slovenia yesterday, June 11th. Report: @Dolenjskanews pic.twitter.com/eG659p60iM
— severe-weather.EU (@severeweatherEU) June 12, 2019
"Most of the roofs of houses were completely destroyed, cars as well - all windows and windshields shattered."
Videos posted onto social media show hailstones the size of tennis balls shredding foliage in gardens as they fall to the ground.
Mr Korosec said: "The biggest I measured was 11cm which was two to three hours after the storm.
VERY LARGE hail in Stari Trg, south Slovenia this afternoon, June 11th! Report: Mišel Podgorski - thank you! pic.twitter.com/GQbo1YgKdS
— severe-weather.EU (@severeweatherEU) June 11, 2019
"In that time they would have melted by 2cm to 3cm so in reality the hailstones were up to14cm in diameter."
Significant damage was dealt to 200 houses in Stari trg ob Kolpi alone, plus others in Prelesje, Deskova vas, Kovaca vas and Predgrad, which are along the border of Slovenia and Croatia.
Scores of firefighters were called out yesterday to help people affected by the storm.
Mr Korosec added: "I was completely shocked to see so many big hailstones there.
"We were expecting very large hail, maybe 5cm to 7cm in some areas - but I never thought I would find hailstones the size of grapefruits."
Mr Korosec, from Sezana, Slovenia, was tracking the storm as part of his job, and said: "Radar images were very impressive and showed there must be very large hail in there.
"The storm was moving over very complex terrain and I wasn't chasing it from very close.
"I waited for it to pass, looked after and found those incredible hail bombs."
The adverse weather conditions also hit the Bavarian region in southern Germany, damaging houses and injuring a seven-year-old boy, according to local media.
Local weather services reported that the region was battered by winds with gusts up 75mph.
Witnesses caught up in the storm filmed hailstones the size of golf balls pummeling the water and thudding on decking around Lake Ammersee.
Verena Weis, who was aboard a boat in the lake when the storm began, told Euronews: "It did not rain at all. The hail came immediately.
"First, everyone was fascinated on board, then worried.
"Many were worried about their cars."
The German Weather Service has issued a level 4 storm warning and warned the public to look out for heavy thunderstorms, gale-force gusts of winds and extremely heavy rain and hail.
GIANT hailstones in Poljanska dolina ob Kolpi, south Slovenia yesterday, June 11th! Report: POLJANSKA DOLINA OB KOLPI / @NeurjeSi pic.twitter.com/fC1NxFpUob
— severe-weather.EU (@severeweatherEU) June 12, 2019
Very large hail in Skrad, NW Croatia yesterday, June 11th! Reporter: Lino Loncaric / @IstraMet pic.twitter.com/Y3mfjTIyVj
— severe-weather.EU (@severeweatherEU) June 12, 2019
GIANT (!!) hailstone from last night's extremely severe hailstorm in Brod Moravice, NW Croatia! June 11th! Photo: Marina Čolić pic.twitter.com/khg7jEgyBF
— severe-weather.EU (@severeweatherEU) June 12, 2019
Comment: View more videos: Giant hailstones hit Munich and Bavaria as storms continue across Germany
Poland was also pummeled:
Italy, Turkey and France meanwhile witnessed huge accumulations of hail: