A wave of mud and debris swept through the small town of Casamicciola Terme early Saturday, engulfing at least one house and sweeping cars down to the sea.
Rescuers recovered the body of a 31-year-old woman, according to Italian news agency AGI, with other local media reporting 13 people had been injured in the incident.
About a dozen people were still unaccounted for early Sunday, according to local official Claudio Palomba. But some people who had earlier been reported missing had since been found safe, including one family with a newborn baby, he said.
Prime Minister Giorgia Meloni tweeted her sympathy to those affected, saying she called an extraordinary cabinet meeting on Sunday to discuss the disaster.
“We are afraid that there might be other victims, but so far the current figure is one dead,” said Luca Cari, a spokesman for the fire service.
The rescue effort was hampered by rain and high winds, which also delayed ferries bringing reinforcements from the mainland.
Heavy rain sent torrents of mud through the streets of Casamicciola Terme, a settlement on the north of Ischia, a lush island near Capri that is thronged with tourists in summer.
The fire service said earlier that one house had been overwhelmed by the mud and two people had been rescued from a car that had been swept into the sea.
In the worst-affected area of the town, at least 30 families were trapped in their homes without water or electricity, with mud and debris blocking the road, ANSA news agency reported.
“The rescue effort remains complex due to the weather conditions,” said the department for civil protection, but it stressed teams would keep working through the night.
The devastation in Ischia comes just weeks after 11 people died in heavy rain and flooding in the central Italian region of Marche.