Cheryl Cole has spent two hours in intensive care after being diagnosed with the deadly disease malaria, according to reports.
The star was taken to the emergency unit at the Cromwell Hospital in west London, the Daily Mirror said.
She was then transferred to the Hospital for Tropical Diseases in the centre of the capital, the paper added, for specialist care.
Cole, 27, was on Tuesday night forced to pull out of the last in the current series of X Factor auditions while she fought the disease.
She contracted malaria on her trip last month to Tanzania - which is home to one of the most dangerous strains of malaria - despite taking malaria tablets.
The singer and close friend Derek Hough spent six days together on Africa's east coast following her split from England footballer Ashley.
Cole, who has been supporting Black Eyed Peas on tour, is reported to have collapsed with suspected gastroenteritis during a photoshoot for her album on Saturday afternoon, when she was initially diagnosed with exhaustion. But she was rushed to hospital the next day after her symptoms, including a soaring fever, worsened.
Cole, who is scheduled to play high-profile shows at next month's V Festival, is expected to get better within a fortnight.
An X Factor spokeswoman said the next stage of the show's auditions would take place at the weekend without the star. She said: "The Manchester auditions will go ahead as scheduled, but Cheryl is unfortunately not able to attend. Simon and Louis will be joined by Nicole Scherzinger."
Malaria is caused by the parasite plasmodium, which is transmitted by the bites of infected mosquitos. If not treated promptly, it can become life-threatening by disrupting the blood supply to vital organs. Nine people die on average in the UK each year from malaria. Around 850,000 die annually around the world, mostly pregnant women and children under five in Africa.