In the rain-drenched southern Ticino region of Switzerland, two people died and four were injured when a mudslide slammed into a small residential building, regional police said.
On the other side of the border, a pensioner and his granddaughter were killed when another landslide engulfed a house on the Italian shores of Lake Maggiore, local media reported.
Three other family members survived.
Those landslides were the latest of many to recently have hit northern Italy and southern Switzerland amid incessant rainfall over recent weeks.
The Italian Liguria region has been doused with as much rain in the first 15 days of November as it normally gets in an entire year.
The tragedies also came a day after storms in southern France left five people dead, when their cars were swept away in flooding.
In Switzerland, the bodies of two local women, aged 34 and 38, were pulled Sunday from the rubble of the three-story apartment building in Davesco-Soragno, near Lugano, after being hit by the mudslide shortly before 2:30am, Ticino police said.
A 44-year-old Italian man, who was living with one of the women, had been dug out and taken to hospital in a critical condition, police told reporters.
Four others in the building at the time it collapsed had escaped with only minor injuries, while the final resident had not been home.
A wall above the building had crumbled under the rain and set off the landslide, police said.
The tragedy came ten days after a 31-year-old mother and her three-year-old daughter were killed when a landslide swept away their house in the same region.
After weeks of heavy rain, southern Ticino has been hit by severe flooding, which worsened when Lake Lugano burst its banks in several places and Lake Maggiore threatened to do the same.
Sea of mud
Just across Lake Maggiore, a 70-year-old man died on Sunday after his house was partially buried in a "sea of mud" unleashed after the rain-doused hill behind the building gave way, Italian media reported.
Rescue workers managed to drag his 16-year-old granddaughter from the rubble after more than four hours of digging but she died later in hospital.
Her parents and grandmother survived.
The family's small, two-storey villa was the only property affected in Cerro, a hamlet on the outskirts of Laveno Mombello, a popular holiday spot.
A neighbour described how he had been awoken during the night by a huge bang "like fireworks".
"Firefighters and civil protection officers were there very quickly and started digging with spades, even with their bare hands," the neighbour told Italian television.
"The parents were helping them . . . it was a horrific scene."
The tragedy means a total of 11 people have died in Italy in accidents related to the freak weather conditions in just over a month.
That toll was expected to rise to 12 later Sunday as rescue workers continued to search for a man whose car was swept off the road by a torrent of water near Genoa, the main city on the Italian Riviera.
Genoa is particularly vulnerable to flooding because the foothills of the Alps climb steeply from immediately around the city.
The city experienced 139 millimetres (five and a half inches) of rain in a matter of hours on Saturday.
The Liguria region has had as much rain in the first 15 days of November as it normally gets in an entire year.
But Italian Prime Minister Matteo Renzi, speaking from the G20 summit in Australia, said the havoc wreaked by the heavy rain was the result of years of neglect of infrastructure.
"We have had 20 years of land management that needs to be scrapped," he said.
An estimated 70 coffins meanwhile were washed away after 50 metres of retaining wall in a cemetery in the Bolzaneto district of Genoa collapsed.
Local residents reported skulls and other bones washing up on the banks of the Polcevera river.
Southern Switzerland has also been soaked, with the Swiss national meteorology institute telling public broadcaster RTS that Ticino had received between 50 and 70 litres of water per square metre in a 24-hour period.
While the rain subsided Sunday, the Swiss government warned that it would pick up again between Monday and Tuesday on both sides of the border, with as much as 100 millimetres expected in some areas.