Blaine's stunt sees him going without food or sleep
David Blaine has begun an attempt to hang upside down for three days.
The illusionist is suspended from wires above New York's Central Park.
Doctors say his latest feat of endurance is particularly dangerous because of the effects of blood collecting around his head.
Speaking to Radio 1 Newsbeat, shortly after the stunt got underway, he said: "This first five hours is infinitely harder than the 44 days I endured in the box in London.
"If I had to chose 44 more days in that box in London or this for five more hours, I would go and sit in that box."
Blaine was referring to his 2003 feat Above the Below where he was suspended above the river Thames in a transparent box.
He has become famous for his quirky record attempts, which have seen him frozen in a block of ice, buried alive and holding his breath for over 17 minutes.
The Dive of Death, as his upside-down stunt is called, involves him going without food or sleep for 60 hours.
Medics regularly check his blood pressure and vision.
One of David Blaine's advisors, vascular surgeon Dr Massimo Napolitano, said the biggest risk was pressure on the eyes, which could lead to blindness.
Blaine demonstrating how he would hang upside-down last week
The only respite the 35-year-old gets is his regular toilet breaks, where he spins round into the upright position.
He is also able to unhook his legs and perform mid-air sit-ups to help relieve the pressure.
"Right now I am trying to figure out how to get the blood circulation into my head because I am getting pins and needles very fast," said Blaine.
The spectacle, in the heart of New York, is already drawing large crowds.
"I think he's a great showman," said Ryan O'Connor from Oregon.
Donna, on vacation from the Isle of Man, added: "He looks very sore to me. He keeps bending and stretching. It looks like he is in a lot of pain."
David Blaine is due to return to earth on Wednesday night.
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