Italy's former prime minister Silvio Berlusconi, aged 83, is in hospital with early-stage double pneumonia after testing positive for coronavirus, the Italian news agency Ansa reports.
He spent the night in hospital in Milan for checks, having tested positive on Wednesday.
Earlier his right-wing Forza Italia party said his condition was not a cause for concern, and "he is fine".
The media tycoon's partner and two of his children also tested positive.
Berlusconi has been in self-isolation with his 30-year-old partner, Marta Fascina, at his villa in Arcore near Milan, after holidaying in Sardinia.
The infection rate in Sardinia – famous for its Emerald Coast beaches – is higher than in much of Italy.
"A small precautionary hospitalisation was needed to monitor the progress of Covid-19 but he is fine," said Forza Italia senator Licia Ronzulli.
Berlusconi was transferred to an isolation ward at San Raffaele Hospital. Double pneumonia – inflammation of both lungs – is a common complication with Covid patients. The disease is generally more severe among the elderly and those with other medical conditions.
Earlier his personal doctor Alberto Zangrillo described him as asymptomatic.
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Berlusconi sent a phone message to party activists in Genoa on Thursday saying "I'm continuing to work as best I can on the current election campaign". Separately, he said he did not know how he had caught the virus.
Italy will hold regional elections on 21-22 September, which had to be postponed at the height of the pandemic in Italy in spring.