LOS ANGELES (AFP) - The humble pantsuit is getting its moment in the sun.

A secret Facebook group called "Pantsuit Nation" that began as 50 Hillary Clinton supporters who decided to wear the outfit to the polls to show their support for the Democratic nominee has blown up into an online phenomenon in recent days.

The invitation-only group now has 2.2 million members and counting.

According to US media reports, Pantsuit Nation was started by Libby Chamberlain, a Clinton supporter in the northeastern state of Maine.

"We talked about how beautifully and stoically Hillary embodies women's fight for equality, and how the pantsuit is an emblem of that struggle," she told CNN.

Clinton has been variously skewered and celebrated for her ubiquitous pantsuits, and in the waning days of the bruising presidential campaign, it's become a quirky symbol for the former secretary of state, first lady and senator.

Pop star Beyonce traded her usual curve-hugging costumes for a pantsuit when she performed at a Clinton rally in Cleveland on Friday. Her backup dancers wore pantsuits in blue, the color of the Democratic Party.

The Facebook page brings together Clinton fans who share personal and often touching stories about why they are voting for her.

One pregnant woman posted a photo from a polling site, saying she was in labour but made sure to vote before going to the hospital to deliver her daughter.

The popularity of the Pantsuit Nation page has now spawned a website (www.pantsuitnation.org), accounts on Twitter and Instagram and a public Facebook page.