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

"I feel incredible," Wallenda said at a news conference in a nearby hotel after completing the tightrope walks. He entered wearing his blindfold, drawing laughter from reporters.

Recalling what made him nervous during his aerial performances, he said strong winds and the unexpected 19-degree angle of the first high wire — he had practised at a 15-degree angle — caused him to hurry his performance.

"That cable looked like it was going straight up," he said.

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.

Nik Wallenda

After completing the first effort, Nik Wallenda embarks on his blindfolded walk along a tightrope between two skyscrapers. (Jim Young/Reuters)

Wearing a bright red jacket, Wallenda tested the tension of the first wire. It took him about six-and-a-half minutes to walk the 138 metes from the Marina City west tower to the top of a building on the other side of the river. The tightrope began at 180 metres from the ground and ended at 205 metres.

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

Televised with a 10-second delay

The next stage of Wallenda's high-wire event he undertook blindfolded — a 30-metre walk 165 metres from the ground between the two Marina City towers. At a fast clip, he made the stretch in little more than a minute.

As he stepped from the wire, he tore off his blindfold and waved; the crowd erupted in cheers.

The Discovery Channel used a 10-second delay for the broadcast, which would have allowed producers to cut away if anything went wrong. Chicago city officials ignored a state law requiring safety nets for aerial acts higher than six metres, saying the law wasn't intended for "elite" performers.

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

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.

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.

Wallenda Chicago Walk

Daredevil Nik Wallenda talks to the media during a press conference after his tightrope walk on Sunday. (Paul Beaty/The Associated Press)

"Yes there's some wind, yes it's cool, but it's not unbearable," he said. Just two days earlier, the city had been beset with gusty winds, snow, hail and driving rain.

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 were asked not to use laser pointers, camera flashes or drones that could interfere. Even grilling was prohibited.

Georgia gorge next in daredevil's sights

Cynthia Garner travelled 144 kilometres from Belvidere, Illinois, with her husband Johnny to watch the event.

"It was amazing. I saw it with my own eyes," Garner said afterward. "I was afraid when he first started, but once I saw that he didn't hesitate and just walked, I wasn't scared for him no more."

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

What's next? Wallenda has said he next wants to recreate a 367-metre-long high-wire walk made famous by his great-grandfather. The stunt at Tallulah Falls Gorge in Georgia included two headstands on the high wire.

"I've trained a bit to do a headstand on the wire, but I've never done it publicly because I've always said if I'm going to do it, I'm going to do it on that walk with him," Wallenda said, explaining that he wants to use vintage film of Karl Wallenda's walk to create the illusion of the two of them sharing the high wire.

"My dream is to actually walk the wire with my great-grandfather," he said. "I get goose bumps and chills thinking about it."