British Airways has told its check-in staff to look out for passengers showing symptoms of the H1N1 virus and to alert doctors who could bar them from boarding a flight, the airline said on Sunday.

The directive was issued in the past "couple of weeks," a spokeswoman for the airline said, explaining that it was part of efforts to limit the spread of swine flu.

"We've given our staff advice in terms of the symptoms to look out for," she said.

RELATED: Why You Should Still Worry About Swine Flu

"If they have any concerns about a passenger when they present for check-in, they have a 24-hour medical number to call and the passenger can then be checked."

Calling the measures "standard practice" for a medical situation, the spokeswoman said only a handful of people had so far been turned away from boarding British Airways flights as a result of the medical checks.

"Obviously with swine flu spreading, we have to be responsible and make sure we do what we can to prevent the disease spreading," she said.

Virgin Atlantic has also adopted similar measures, according to the Sunday Times newspaper. Officials from Virgin Atlantic were not immediately available to comment.

A group of 52 British school children and their teachers were quarantined in Beijing on Saturday after four pupils were admitted to hospital infected with the virus. Another four pupils have since had to be admitted for treatment.

The group arrived in China last week for a culture and study tour. But shortly after arrival at Beijing airport, four of the students — all believed to be teenagers — were admitted to hospital showing symptoms of swine flu infection.

British authorities confirmed this week that 29 Britons infected with the H1N1 virus had died, with officials making plans for up to a third of the population to fall ill.

In total there are an estimated 55,000 new cases of swine flu in Britain a week, although in the vast majority of cases the symptoms are mild.

The pandemic has killed around 430 people worldwide, according to the World Health Organisation (WHO).