At least 12 people are reported to be missing on the island in the Bay of Naples, which has also suffered from flooding. Two people were rescued from a car after it was dragged into the sea, the fire service said.
Italy’s infrastructure minister Matteo Salvini initially said eight people had been killed in the landslide. But interior minister Matteo Piantedosi later contradicted this, insisting there were no confirmed deaths.
“The situation is very complicated and very serious because probably some of those people are under the mud,” Mr Piantedosi told public broadcaster RAI from an emergency command centre in Rome.
Some 30 families were stranded by the landslide, Naples prefect Claudio Palomba was quoted by La Repubblica as saying, with at least 10 buildings also reported to have collapsed.
One family with a newborn which was previously feared missing was eventually located and was receiving medical care, Mr Palomba said.
Reinforcements were being sent from Naples but were having some difficulties reaching the island with motorboats and helicopters due to bad weather, the fire service said.
At least 120mm of rain fell on the island, local media quoted civil protection minister Nello Musumeci as saying, and footage showed a torrent of mud and debris having partly destroyed homes and vehicles.
The force of the mud sliding down mountainsides was strong enough to send buses into the sea at the port of Casamicciola, at the north end of the island. Streets were impassable and mayors on the island urged people to stay at home.
Prime minister Giorgia Meloni said she was in close contact with the civil protection minister and authorities in the Campania region “to follow the evolution of the wave of bad weather that has hit Ischia”.
“The government expresses its closeness to the citizens and mayors of the municipalities on the island of Ischia and thanks the rescuers engaged in the search for the missing”, Ms Meloni said.
Ischia is a volcanic island situated around 19 miles from Naples, which draws both domestic and foreign visitors to its thermal baths and picturesque coastline.
It is densely populated and has a large number of illegally built houses, putting inhabitants at permanent risk from flooding and earthquakes. In 2006, a landslide killed a father and his three daughters on the island.
The south of Italy, where houses are often built illegally in unsafe areas, is susceptible to fatal landslides. In 1998, at least 150 people were killed when mud submerged the village of Sarno, also not far from Naples.
Additional reporting by agencies