Hillary Clinton ducked a thrown shoe, expressed surprise, cracked a couple of jokes and continued her keynote speech on stage in front of a Las Vegas convention audience.

Moments later, still in the stage spotlight, the former secretary of state reflected calmly on what she called "an atmosphere and attitude in politics" that she said rewards inflexibility and extremism.

Meanwhile, a woman was taken into federal custody after admitting she threw the shoe. She did not say why she did it.

"Is that somebody throwing something at me?" Clinton said after the object flew past her on the stage at the Mandalay Bay resort on Thursday, according to the Associated Press.

"Is that part of Cirque de Soleil [circus arts and street entertainment]?"

Brian Spellacy, US Secret Service supervisory special agent in Las Vegas, said the woman in custody was being questioned and would face criminal charges.

Black and orange shoe

A black and orange athletic shoe was recovered from the stage, Spellacy added.

Ilene Rosen, who was seated in the second row, said she saw an orange object fly towards the stage from a side aisle and papers fluttering in the air.

Rosen said the woman had walked to a rope line within six rows of the front of the seating area, threw the items, turned around, put her hands in the air and walked up the aisle towards the back of the room.

Security officers quickly caught up with her. In the hotel hallway, the middle-aged blonde woman sat calmly on a sofa, wearing a blue dress and sandals.

She said she threw a shoe and dropped some papers, but did not identify herself to reporters or explain the action.

Spellacy and Mark Carpenter, spokesman for the recycling institute, said the woman was not a credentialled convention member and was not supposed to have been in the ballroom.

The shoe-throwing incident reminded some of former President George W. Bush dodging two shoes thrown by an Iraqi journalist during a news conference in Baghdad in December 2008.

Clinton, the former first lady and Democratic senator from New York, has been travelling the country giving paid speeches to industry organisations and appearing before key Democratic Party constituents.

During a speech in San Francisco on Tuesday, Clinton said she was seriously considering a presidential bid and all it would entail.