Siblings from a famed circus family - the Flying Wallendas - walked a wire strung 25 stories over New York's Times Square Sunday, in a hair-raising balancing act performed across five city blocks.

"If you can make it in New York you can make it anywhere - so let's make it in New York," Nik Wallenda, 40, told his sister Lijana before they began the fearsome feat.

The undertaking, which was broadcast live, saw the duo start the wire walk on opposite sides, slowly moving towards each other holding balancing poles as a throng of onlookers gawked from below.

When the siblings met, Lijana sat on the 396-meter wire strung between skyscrapers so her brother could step over her, before standing back up and finishing the walk.

Tensions were running particularly high as it was the 42-year-old Lijana's first such attempt since 2017, when she and four others fell more than nine meters while rehearsing an eight-person pyramid on a wire.

The near-fatal incident left her seriously injured, including breaking most bones in her face.

During the approximately 36 minutes the acrobats took to complete the nerve-wracking stunt Nik - who in 2012 traversed Niagara Falls on a wire, and the Little Colorado River Gorge close to the Grand Canyon a year later - offered words of encouragement to his sister via earpiece microphones, as she audibly prayed and sang.

New York allowed the siblings to attempt Sunday's walk on the condition that they wear safety harnesses, a mandate Nik said added physical weight and stress to the challenge.

In 2013 the city had declined him permission to cross a wire anchored between the Empire State and Chrysler buildings.