Singers Alesha Dixon and Pixie Lott said it was an "absolute honour" as they performed at the launch of the Royal British Legion Poppy Appeal.
The pair, who are the faces of the Poppy Appeal 2012, were cheered by crowds in Trafalgar Square in London as they headlined a free concert to launch the Legion's annual fundraising drive.
"It is such an honour to be performing here in Trafalgar Square," Lott told the crowds before performing a series of hits including Mama Do and It's All About Tonight.
"Thank you for coming down for such a great cause as the Poppy Appeal. It is a privilege to be here," she added.
Dixon, a Britain's Got Talent judge, said it was an "absolute honour" to perform at the launch event. She joked with the crowds as she performed a series of hits including The Boy Does Nothing and Breathe Slow. "If it gets really rock 'n roll feel free to jump in the fountains because that always works," she quipped.
The concert featured military bands The Corps of Drums of the 1st Battalion Coldstream Guards, the 1st Battalion Irish Guards and the trumpeters from the Band of the Grenadier Guards.
The appeal's £42 million target is up on the record £40 million raised last year. People wishing to donate can do so at any time online or by text.
Poppies will go on sale from Saturday until November 11, at locations across the country including train and Tube stations and shopping centres.
The act of observing a two-minute silence each year on November 11 began in 1919, following the Armistice agreement between the Allies and Germany at 11am on November 11, 1918, the end of the First World War.
The Royal British Legion spends £1.7 million a week on care and support for military families, including grants, employment advice and funding, emotional support, tribunal and inquest advice, care homes and family breaks.