More than 50 Britons were in quarantine tonight after five schoolchildren were diagnosed with swine flu during a trip to China.
The teenagers from London were being treated for the H1N1 virus in a Beijing hospital having arrived in China earlier in the week.
A further 52 pupils and teachers, who were understood to have been in close contact with the five, were ordered to stay inside their hotel under strict quarantine procedures.
The year nine (aged 13-14) children taken ill in China were from the Central Foundation Boys School in Clerkenwell and Parliament Hill School in Camden, organisers said.
The quarantined group was among a party of around 600 British students and teachers from across the UK who had travelled to China.
Organised by the Specialist Schools and Academies Trust, the British Council and Hanban, a Chinese organisation linked to Confucius Institutes, and part-funded by the Department for Children, Schools and Families, the two-week trip was intended to enable the teenagers to learn more about the country's culture and language.
A spokesman for the Specialist Schools and Academies Trust said: "We can confirm that four students from London on a Chinese language, learning and cultural visit to Beijing have been diagnosed with swine flu.
"They are making an excellent recovery and being looked after very well by hospital staff.
"The students are part of a trip to China organised by Hanban (a Chinese non-government organisation).
"The SSAT has worked with Hanban to enable schools from England to participate in this cultural visit.
"We hope the students make a quick recovery and can join their peers on the rest of the visit as soon as possible."
The spokesman added that it was a "terrible shame" for the students in quarantine but efforts were being made to enable them to join in activities at the hotel and to to contact their families.
Meanwhile, the Department of Health issued holiday advice for people with swine flu, recommending delaying travel until symptoms, which include high temperature, have gone.
Holidaymakers should take medication such as paracetamol with them and avoid public places if they get swine flu.
People travelling to Europe should carry a European Health Insurance Card (EHIC), the DoH said.
Health Secretary Andy Burnham said: "I want families to go on their holidays and have a great time this summer, and mums and dads shouldn't worry unnecessarily about swine flu.
"But, just as they would anyway, parents should keep a close eye on their children's health."
Among the pupils are four teenagers from Clevedon School in North Somerset, who were in China with two teachers.
They said in an e-mail sent from the hotel room, and reported by the BBC: "We are quarantined in the hotel and are all currently well as we have daily temperature checks which are all good."
Pupil Christopher Hicks said the party were exploring the Great Wall of China when they were recalled on the grounds that they had been in contact with another child with swine flu.
They said they had their own rooms, but had to wear face-masks and were limited to a restricted zone.
Another boy Joe Robinson wrote: "We're being treated very, very well. The food's great. We've got our own individual tellies."
Four girls from Cheltenham Ladies' College have also been quarantined.
One of the pupils, 15-year-old Lucy van Amerongen is finding the experience "quite intimidating", her sister Amii told the Gloucestershire Echo.
Her sibling told the paper: "Lucy called me this morning telling me that she is confined in a hotel and she is being very brave about the whole thing.
"She said it was quite intimidating - they have these 'guns' that they point at your head which measure your temperature."
Her TV producer father Victor van Amerongen, 54, who lives near Stroud, Gloucestershire said he believed his daughter could be kept under the restrictions for up to a week.Reuse content