An apparently healthy six-year-old girl from west London has died of swine flu. She is the first child in Britain without underlying health problems to be killed by the virus.

Chloe Buckley, who lived in West Drayton, died at St Mary's Hospital in Paddington a day after her doctor is reported to have wrongly diagnosed her illness as tonsillitis.

It is alleged that Chloe was taken to her GP with a sore throat on Wednesday but was sent home without being prescribed antiviral flu drug Tamiflu. Her condition deteriorated overnight and her parents Michael, 40, and Jacinta, 37, rushed Chloe to Hillingdon Hospital in Uxbridge on Thursday morning.

She was transferred for emergency treatment to St Mary's but died a few hours later. She was due to celebrate her seventh birthday on Friday.

Sara Benn, headteacher of St Catherine's RC primary school where Chloe was a pupil, said today: "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 and will be missed by her fellow pupils and teachers at the school. Our thoughts are with the parents and family at this time. We are working with the council and health authority to support parents and pupils dealing with this devastating news."

Provisional tests revealed Chloe had contracted swine flu and a post-mortem examination being carried out today is expected to confirm the cause of death.

Chloe is only the second person in Britain to have died of the illness despite not suffering any other health issues. Her death will spark widespread fears that the virus is increasingly potent. A mother with a child at the same school said today: "Chloe was fit and healthy and in school on Monday and Tuesday. By Wednesday she had developed a very sore throat and her mother took her to the doctor.

"But the doctor said she had tonsillitis and sent her home without giving her Tamiflu."

Her parents, who are "devastated" by the death, are being looked after by the local health trust. The couple, who have been married for 15 years, are understood to have two other children — boys aged 10 and 12.

Many of the girl's classmates were being kept at home today amid fears swine flu could sweep through the school. Parents were understood to have been sent letters today notifying them of Chloe's death.

A spokeswoman for Hillingdon Hospital said: "It is with great sadness that we heard about the death of Chloe Buckley. A post-mortem will be carried out on Chloe to identify if she had any underlying health conditions and to determine the cause of death."

A spokesman for NHS London said they could not confirm whether Chloe had been sent home from her GP after being diagnosed with tonsillitis.

Simon Tanner, regional director of public health for London, confirmed Chloe had caught swine flu in this country.

He said: "The Health Protection Agency is now seeing large numbers of people with the virus in the community. In London we have a steeply rising number of cases."

He said despite Chloe's death swine flu continued to be a mild illness in the vast majority of cases. He added: "We would like to extend our deepest sympathies to the family at this difficult time as they come to terms with their loss."

He said Chloe's death will not change the way the virus is being tackled. "We will not change the advice we are giving out. The fact the virus is spreading in the community means everyone has a chance of getting it as they go about their normal lives. This will probably not be the last death."

The family are understood to be devout Catholics. Their church, St Catherine's, refused to comment this afternoon.

Chloe is the 16th person to die from swine flu in Britain although 14 deaths have been attributed to underlying health problems.

There are almost 10,000 confirmed cases of swine flu in the UK — the third-highest in the world behind Mexico and the US — although the total number is likely to be far higher.

GPs' surgeries across London were today told to prepare for a "swine flu panic" as thousands seek advice after the deaths of Chloe and the first otherwise healthy patient, believed to be a middle-aged man from Essex, on Friday.

Dr Laurence Buckman, chairman of the British Medical Association's GP committee, said: "We will see a rise in the number of people wanting to see a doctor. A lot of people will be scared as a result of this case."