Italian former prime minister Silvio Berlusconi, dubbed "the immortal" for his longevity in politics, was "stable" Thursday after a night in intensive care, according to a minister from his party.

The 86-year-old media mogul and senator, who has been in and out of hospital in recent years, was admitted Wednesday to the cardiac unit at Milan's San Raffaele Hospital for reported respiratory problems.

Foreign Minister Antonio Tajani, a member of Berlusconi's Forza Italia party, told Rai Uno radio that he had spoken to the magnate's doctor.

"He told me Silvio Berlusconi had a quiet night, his condition is stable," he said.

Tajani had earlier said Berlusconi was in intensive care "because of a problem concerning an unresolved infection".

Italy's best-selling Corriere della Sera daily said the magnate has been diagnosed with leukemia.

Berlusconi was rushed to hospital after complaining of breathing difficulties and had low blood oxygen levels which put his cardiovascular and respiratory systems under stress, Italian media reported.

The billionaire leader of the right-wing Forza Italia party spent four days last month at the same hospital for what Italian news reports called heart issues, before being discharged last Thursday.

"I have already started working again... ready and determined to commit myself, as I have always done, to the country I love," he said in a message posted on social networks Friday.

And on Sunday, he posted a photo of himself grinning in front of a vast lawn of tulips in his villa in Arcore, in northern Italy.

After dominating Italian politics for decades, the "Cavaliere" as he is widely known in Italy, now appears physically diminished on the rare occasions he is seen in public.

Long gone are the days of his infamous erotic "bunga bunga" parties with young starlets, which he has always insisted were nothing more than elegant dinners.

Forza Italia is a member of Prime Minister Giorgia Meloni's right-wing coalition government, although the party attracts only about 10 percent of voters.

Meloni tweeted her "sincere and affectionate wish for a speedy recovery" Wednesday, while Matteo Salvini, whose League party is also a coalition member, tweeted "Forza Silvio, Italy is waiting for you!"

Berlusconi entered politics in 1994 and for millions of Italians he represented a golden age of the Italian economy and the self-made man.

Despite a series of sex scandals and court cases which threatened to tarnish his image, he has held a soft spot in many Italians' hearts since then.