A 12-year-old girl is among five people in the UK who have contracted swine flu after visiting Mexico, the Prime Minister, Gordon Brown, has confirmed.
Two adults - one from Birmingham and one from London - are also undergoing treatment, as are the two previously confirmed cases in Scotland.
The girl's school, Paignton Community College in Devon, has shut and pupils will be offered anti-viral drugs.
Mr Brown said all those with the virus were responding well to treatment.
The number of swine flu cases globally is rising and the US has confirmed that the death of a 23-month-old child there is the first fatality outside Mexico.
In Scotland, the BBC understands that tests proved negative on seven people who had come into contact with a couple from Polmont, near Falkirk, who were the UK's first confirmed cases.
The results of tests on two more of the original contact group relating to Dawn and Iain Askham are still pending.
Mr Brown revealed the latest cases at Prime Minister's Questions. All of those affected have travelled recently from Mexico, Mr Brown said.
"All of them have mild symptoms. All of them are receiving and are responding well to the treatment that has been effective so far, the use of Tamiflu [anti-viral drug]," he said.
The UK was taking "the preparations that are necessary and the precautions to prevent the incidence of this disease in this country", the prime minister added.
This included enhanced airport checks, expanding anti-viral stocks from 35 million to 50 million, ordering extra face masks and printing an information leaflet for every family, he added.
Delivery of public information leaflets is expected to begin within days, as part of planned measures to cope with potential pandemics.
However, the Conservatives have hit out at the government because a national pandemic flu helpline set out in the government plans is not expected to be operational before the autumn.
Shadow health minister Stephen O'Brien said the line would be crucial in giving people access to information and medication without having to visit GPs or hospitals.
The World Health Organization (WHO) has raised its alert status to level four - two levels from a full pandemic - after concluding there had been sustained transmission between humans.
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