Fears that a swine flu crisis is escalating in Britain grew as the virus claimed the lives of a seemingly healthy six year-old girl and a family doctor.
Chloe Buckley, from West Drayton, Middlesex, was described as "perfectly healthy" in the days before she first started feeling ill.
She saw her GP last Wednesday complaining of flu-like symptoms and died the following day.
On Saturday, Dr Michael Day, 64, from Bedfordshire, also died after contracting swine flu.
Tests have proved that both contracted the H1N1 virus - or swine flu - and post mortem examinations are now being carried out to determine the exact cause of death.
If they are found to have died of swine flu, rather than other underlying causes, it will take the number of deaths in healthy patients to three, after another person died on Friday.
Speaking after news of Chloe's death, Simon Tanner, regional director of public health for London, warned: "The Health Protection Agency is now seeing large numbers of people with the virus. This will probably not be the last death."
Nearly 10,000 Britons have been confirmed with swine flu but hundreds of thousands more are feared to have the virus. It has been linked to 17 deaths.
The Government has warned that the number of swine flu cases could soar to 100,000 a day by the end of next month and estimated that the virus could eventually affect up to 50 per cent of the population
Enough swine flu vaccine has been ordered to cover the entire population, with the first doses arriving next month and half of all doses expected to be given by the end of the year.
A spokesman from NHS London would not disclose on Monday whether Chloe had been treated with the antiviral flu drug Tamiflu.
St Catherine's Roman Catholic Primary School, in West Drayton, where she was a pupil has been closed for summer early despite national guidance it should remain open.
Chris Spencer, director of education and children's services at Hillingdon Borough Council, said: "It's an exceptional set of circumstances, this is a little girl who until a few days ago in all our minds was a child that was perfectly healthy."
Chloe, who was due to turn seven on Friday was the youngest child of devout Roman Catholic parents Michael, 40, and Jacinta, 37. Sara Benn, headmistress of St Catherine's, said: "It is impossible to put into words the sorrow that the whole school feels in such tragic circumstances.
"Chloe was a bright and tenacious student with a keen interest in sports. She will be missed by her fellow pupils and her teachers at the school. Our thoughts are with her parents and family."
Dr Day, a married father-of-five who lived in Stanbridge, Beds., is understood to have been suffering with a bit of a cold in the days before his death but was taken into Luton and Dunstable Hospital on Saturday and died the same day.
A local GP since 1974, he had retired, but worked as a locum and carried out private work. All patients who had been in recent contact with him are being clinically assessed.
Dr Paul Hassan, senior partner at Priory Gardens Health Centre, said: "This news has come as such a shock to us all and we are completely devastated. Dr Day was a work colleague and also a personal friend to everyone at the practice."
One neighbour said: "There had been no signs of him being ill. All I heard was that he had a bit of a cold before he went into hospital."
Dr Laurence Buckman, chairman of the BMA's GPs Committee, offered his condolences to Dr Day's family but said it was necessary to stay calm.
"It is very important that members of the public do not panic, and continue to follow health advice about swine flu and managing it if they are infected.
"The vast majority of people will recover quickly by taking paracetamol or ibuprofen, and drinking plenty of fluids."
Andy Burnham, the Health Secretary, said: "I offer my sincere condolences to the families of Dr Michael Day and Chloe Buckley at this very difficult time.
"Although the swine flu virus is proving generally mild in most people, in some cases it is more severe. Unfortunately, as with seasonal flu, people may develop complications and in some cases will die.
"The Government has been planning for such an outbreak for a number of years and we are amongst the most prepared countries in the world.
"We have been working closely with the Royal Colleges and staff bodies to protect and prepare frontline health workers, who are at the heart of our response to this outbreak, whilst providing the best health care possible to patients."
He advised anyone who thinks they may have swine flu to check their symptoms on www.nhs.uk or call the swine flu information line on 0800 1 513 513.