The "French Elvis" was holidaying on the Caribbean island of Saint Barthélemy, a millionaires' playground where he owns a house, when he was taken ill and flown to a hospital on the nearby island of Guadeloupe.
The clinic in the French island's capital Pointe-a-Pitre gave no details about his illness but said in a statement he was stable in its intensive care unit and that a transfer to an unstated destination was being organised.
Hallyday's producer Gilbert Coullier said the 69-year-old star was being treated for a case of "persistent bronchitis" and denied reports that the quiffed, leather-clad singer had suffered heart problems.
French radio reports said he was holidaying on Saint Barthélemy when on Saturday he had a bout of tachycardia – an abnormally fast heartbeat that is
sometimes caused by excessive alcohol or drugs intake.
Hallyday was taken to Pointe-a-Pitre, where his young wife Laeticia was with him.
The star's son David Hallyday said on his Twitter account that regarding his father's health: "The news is good and that reassures us enormously."
The latest incident came two and a half years after a health scare in Los Angeles that nearly killed France's top rocker, who is currently on his fifth marriage.
Hallyday, who last year had his artificial hip replaced, had emergency surgery and was put into an induced coma in late 2009 after falling ill on a flight to Los Angeles from Paris, where he had a hernia operation days before.
He attempted suicide in 1966, and collapsed on stage in 1986. In a 1998 interview he admitted taking cocaine and suffering a difficult childhood with an alcoholic father.
Though little known and sometimes ridiculed abroad, Hallyday has sold more than 100 million albums and played 45 major tours in a career that began in the 1960s. He is currently in the middle of another major tour.
Despite being a French national icon, Hallyday moved to Switzerland in 2007, becoming a symbol of an exodus of high-earners fleeing France's relatively high tax rates to neighbouring jurisdictions.