A 14-year-old girl has died after being given a cervical cancer jab as part of a national immunisation programme, but the exact cause of death is unknown.
The pupil took ill at Blue Coat CofE School in Coventry shortly after she received the Cervarix vaccine. She died in the town's University Hospital.
The batch of the vaccine used has been quarantined by the local NHS.
The injection offers protection against a sexually transmitted disease, which is linked to most cervical cancers.
A routine programme of vaccinating 12- and 13-year-old girls started in September 2008 across the UK using the Cervarix vaccine made by GlaxoSmithKline. A catch-up campaign is now under way for older girls.
The injection offers protection against the human papilloma virus (HPV), the most common cause of cervical cancer.
The girl, who has not yet been named, died at lunchtime on Monday.
We are conducting an urgent and full investigation into the events surrounding this tragedy Dr. Caron Grainger
Dr Caron Grainger, joint director of public health for NHS Coventry and Coventry City Council, said their sympathies are with the girl's family and friends.
She said: "The incident happened shortly after the girl had received her HPV vaccine in the school. No link can be made between the death and the vaccine until all the facts are known and a post-mortem takes place.
"We are conducting an urgent and full investigation into the events surrounding this tragedy."
A small number of girls at the school had also reported mild symptoms such as dizziness and nausea but they were not admitted to hospital.
In a statement posted on the school's website, headteacher Dr Julie Roberts said during the immunisation, "one of the girls suffered a rare, but extreme reaction to the vaccine".
"A number of other girls also reported being unwell and some were sent home," she said.
"If your daughter has received a vaccine today we ask that you are extra vigilant regarding any signs or symptoms."
She listed possible reactions as mild to moderate short-lasting pain at the injection site, headache, muscle pain, fatigue and a low-grade fever.
It is thought about a million girls have already safely received the vaccine.
When the national immunisation project was announced, there was some controversy about the selection of Cervarix over Gardasil, which is used by the majority of vaccination programmes worldwide.
It is important we have the results of further investigations as soon as possible to establish the cause of this sad event Department of Health
Q&A: The cervical cancer vaccine
Dr Pim Kon, medical director at GlaxoSmithKline UK, which makes Cervarix, said: "Our deepest sympathies are with the family and friends of the young girl.
"We are working with the Department of Health and MHRA (Medicines and Healthcare products Regulatory Agency) to better understand this case, as at this stage the exact cause of this tragic death is unknown."
The global pharmaceutical company added that the vast majority of suspected adverse reactions have related either to the symptoms of recognised side effects or were due to the injection process and not the vaccine itself.
Public health minister Gillian Merron said: "Our deepest sympathies are with the family. It is important we have the results of further investigations as soon as possible to establish the cause of this sad event."
In the UK, about 3,000 women are diagnosed with cervical cancer every year and about 1,000 die from it.
The department said Cervarix had a strong safety record.
Shadow Health Secretary Andrew Lansley said the tragedy needed to be investigated "as a matter of urgency".
He said: "This again raises the question which we have asked for some time, as to why the government won't publish the assessments it made of the relative merits of the two HPV vaccines and why we therefore use a different vaccine to most other comparable countries."
There are more than 100 types of HPV but only 13 of them are known to cause cancer.
Cervarix protects against two strains of HPV that cause more than 70% of cases of cervical cancer in women.
Vaccination is not compulsory and consent is required before it is administered to the under-16s.
I am so angry. This does not have to happen.
If they try to say "no association" there should be rioting in the streets.