Pop star Michael Jackson was taken by ambulance to a Los Angeles-area hospital Thursday afternoon, according to the Los Angeles Times.
The singer was reported to be in cardiac arrest and paramedics had to perform CPR in the ambulance.
Later reports say he had stopped breathing.
Police in Los Angeles have blockaded streets around Cedars-Sinai Medical Center in Los Angeles.
The singer was preparing to begin touring again, including a concert series at London’s O2 arena — in his first tour since 1997.
Jackson, whose hits include Thriller and Billy Jean, has been rehearsing in the Los Angeles area for the past two months.
There had been recent reports that Jackson was in poor health and his London concert series, billed as a farewell to London, was postponed by a few days.
However, the concerts quickly sold out, a testament to the enduring appeal of the singer known as the King of Pop.