A 19-year-old man has died after contracting swine flu in London, health authorities in the capital have said.
The man, from south London, had serious underlying health problems and was in Lewisham Hospital. Tests undertaken after his death showed he had the flu.
He is the fourth person with swine flu to die in the UK. Dr Simon Tanner, from NHS London, said London has seen a "spike" in flu cases in the past week.
London is the second-worst affected area, with more than 1,900 cases.
Rise in cases
The death comes as the government's Chief Medical Officer Sir Liam Donaldson warned the public to avoid panic buying "counterfeit" anti-swine flu drugs online.
Dr Simon Tanner, regional director of public health for London, said: "It is with sadness that we have to announce the death of a patient in London who has subsequently tested positive for H1N1 swine flu."
He said no further details about the patient would be released.
"There are people out there in the community, and we've talked about one today - precious individuals that have got really difficult medical conditions - who are particularly vulnerable when the population has a virus like this in it," he said.
"We've had a spike in London and in the last week or so we've had larger numbers every day."
Sir Liam said the UK has moved beyond the stage of containing the flu into the "treatment phase", and advised people not to resort to self-medication.
Earlier experts warned that the number of cases in the UK could rise to 100,000 a day by the end of next month.
Jacqui Fleming, 38, of Glasgow, was the first person in the UK to die after contracting the flu, followed by a 73-year-old man from the Inverclyde area of Scotland.
The youngest victim was six-year-old Sameerah Ahmad in Birmingham. All fatal cases were suffering from other health problems.
The first case of the flu in the UK was reported in April.