Daredevil Nik Wallenda wowed Chicago and the world Sunday with two hair-raising skyscraper crossings on the high wire without a safety net or a harness.

Thousands of cheering fans packed the streets around the city's Marina City towers to watch the 35-year-old heir to the Flying Wallendas' family business complete the back-to-back walks including one wearing a blindfold.

As he stepped from the wire after completing the second leg, he tore off his blindfold and waved to the crowd of thousands below who erupted in cheers.

The spectacle was telecast almost-live on the Discovery Channel so producers could cut away if Wallenda fell.

Wearing a bright red jacket, Wallenda tested the tension of the wire around 6 p.m. It took him about six and a half minutes to walk the wire at a 19-degree incline from the Marina City west tower to the top of a building on the other side of a river.

"I love Chicago and Chicago definitely loves me," said Wallenda as he walked the wire, with the crowd of thousands below him screaming in support. "What an amazing roar!"

The next stage of Wallenda's high-wire event he undertook blindfolded -- a walk between the two Marina City towers, Chicago landmarks with Hollywood credits. At a fast clip, he made the stretch in little more than a minute.

The Discovery Channel used a 10-second delay for the broadcast, allowing producers to cut away if anything went wrong.

At around 6:40 p.m., just minutes before the anticipated start of his high-wire feat, Wallenda, who lives in Florida, said the chilly conditions in Chicago would not stall him.

"Yes there's some wind, yes it's cool, but it's not unbearable," he said.

Months of preparations have meant helicopters lifting cable to the rooftops, road closures and clearances from the Federal Aviation Administration and U.S. Coast Guard. Residents of Marina City have been asked not to use laser pointers, camera flashes or drones that could interfere. Even grilling has been prohibited.

Two of his previous televised tightrope walks -- over the brink of Niagara Falls in 2012 and across the Little Colorado River Gorge in 2013 -- drew about 13 million viewers each.

The Discovery Channel hoped to capture an elusive real-time audience in the DVR era. The network plans to keep the almost-live telecast of Wallenda's progress on viewers' TV screens even during the commercials, using a "double box" that will show advertisements and Wallenda simultaneously.

The Marina City towers have been on screens -- Steve McQueen chased a fugitive around the west tower's corkscrew parking ramp in "The Hunter" -- and graced the album cover of Wilco's 2002 "Yankee Hotel Foxtrot."

Hours before the tightrope walk, Scott Jensen of Schaumburg, a Chicago suburb, waited to watch the spectacle with his 15-year-old son, Matthew, and Matthew's friend Tommy Demaret, also 15. They were bundled up and eating sandwiches while seated on a concrete planter with a nearly straight-overhead view of the high wire.

"I think anybody who does something like this is crazy and it's a once-in-a-lifetime opportunity to see it," Scott Jensen said.

Cynthia Garner traveled 90 miles from Belvidere, Illinois, with her husband Johnny.

"I'm scared of heights," Garner said looking up at the wire.

"The feeling I feel when I look up there is scared for his life," she said. "I'm scared for his life."

Journalists covering Sunday's event signed waivers relinquishing their right to claim emotional distress if they witness a catastrophe.

A year before Wallenda was born, his great-grandfather fell to his death during a tightrope stunt in Puerto Rico. He was 73.

Wallenda says after Chicago he wants to recreate a 1,200-foot-long high-wire walk made famous by his great-grandfather. Karl Wallenda's stunt at Tallulah Falls Gorge in Georgia included two headstands on the high wire.

"Life is on the wire," Karl Wallenda once said. "Everything else is just waiting."