The giant hailstones smashed through windows and car windscreens and damaged roofs in Pescara, as well as leaving people with bruising and head injuries, local media reported.
At least 20 people were taken to hospital in the city for treatment, with many reportedly requiring stitches.
A video taken from inside a boat moored at Pescara's port showed the huge hailstones splashing into the sea.
Streets and buildings in the city of Pescara, including the hospital, later flooded as intense rain followed the hail.
Local media reported several people narrowly escaping cars swept away by floodwaters.
Many people injured, the city is in state of emergency. Here is the glass of my car, broken by these ice bullets…as well as the roof of the university. I could never imagine something like this can happen, surely not here in #Pescara #Italy #ClimateCrisis #ClimateEmergency pic.twitter.com/uKQHQegesa
— Piero D'Incecco (@piero_dincecco) July 10, 2019
City mayor Carlo Masci declared a state of emergency in Pescara on Wednesday and said many roads in the city were “impassable.”
— WEATHER/ METEO WORLD (@StormchaserUKEU) July 10, 2019
There was widespread flooding in other Adriatic coastal towns and resorts, including Senigallia in Marche, while 200 pine trees were felled by high winds near Ravenna.
Weather alerts were issued for most parts of Italy on Tuesday and Wednesday as almost every region experienced high winds, hail, or rain.
The sudden downpours came after weeks of sticky heat across the country.
Parts of the south escaped the storms and remain hot, particularly Sicily, where several fires have broken out on the island as it bakes in extreme heat.