The famed magician David Blaine checked in for a week-long stay at Lincoln Center yesterday, but his accommodations are anything but comfortable.

Armed with little more than an oxygen tube, a pair of pants, goggles, and a catheter, Mr. Blaine lowered himself into an 8-foot sphere filled with water shortly after 1 p.m. and began his latest stunt aimed at defying physics and wowing the public.

If all goes well, Mr. Blaine’s week under water will lead up to a second stunt on Monday, when he plans to briefly exit the tank, lock himself in 150 pounds of chains, and slip back in. Testing his multi-tasking skills, he’ll then try to escape from the bottom of the tank in one, nine-minute breath, which would simultaneously set a world record in breath-holding. “I’ll get out, or I’ll die,” Mr. Blaine, 33, told hundreds of onlookers yesterday before entering the water. The finale is to be broadcast live on ABC in a special titled “David Blaine: Drowned Alive.”

Living underwater for a week is the latest “death-defying” trick for Mr. Blaine, whose previous exploits have included burying himself alive for a week, freezing himself in a block of ice for more than 61 hours, and balancing atop a 90-foot pillar for 35 hours. In his most recent stunt, in 2003, Mr. Blaine lived on nothing but water while suspended for 44 days in a box high above the Thames River in London.

Mr. Blaine has been training for the underwater breath-holding record since early December, his coach, Kirk Krack, said. A German, Tom Siestas, is the world record holder, at eight minutes, 58 seconds. Mr. Blaine was slightly under eight minutes in his training, Mr. Krack said.

Mr. Blaine’s doctor, Murat Gunel, the chief of neurovascular surgery at Yale University, advised against the week-long stunt. “What he told me was, ‘Whether you like it or not, I’m going to do it.'” Dr. Gunel said. He is leading a team of technicians and paramedics who will scrutinize Mr. Blaine as best they can during his time in the tank. Still, the magician has shunned a hookup that would allow doctors to monitor his heart rate.

The health concerns are many, Dr. Gunel said. In submerging himself in water for so long, Mr. Blaine risks nerve damage, blackouts, and hypothermia, as well as a serious case of pruned fingers.The subsequent challenge of holding his breath for several minutes would deprive his brain of oxygen and could lead to a stroke.

After entering the tank yesterday afternoon, Mr. Blaine made hand signals and posed for photos for the spectators who lined up to see his stunt. For many, the first question was, “How does he go to the bathroom?” The catheter answered half of that query, and a diet consisting exclusively of liquid nutrients solved the other half. As for communication, Mr. Blaine and his technicians and doctors exchanged hand signals and notes written on water-resistant white boards. At times, he will also wear a helmet that will allow him to speak – and even to sleep.

Technicians send the nutrients – taken orally – and other items to Mr. Blaine through a 30-inch hole at the top of the tank.

For onlookers who lingered to watch Mr. Blaine, the spectacle of a man submerged in a tank of water proved captivating. “He’s like a new-age Houdini,” a student at nearby Fordham University, Greg Balla, said. Still, Mr. Balla had his doubts about whether Mr. Blaine could last the full week. “It seems like a good idea now, but three or four days from now, he might freak out.”

Teddi Steinberg of the Upper West Side was more confident.”He’ll need a dermatologist after one week, but he’ll be no worse for the wear.”