The 37-year-old man was discovered lying on the floor of his second-story apartment at 710 E. 13th St. near Avenue C, after a fire started there at about 2:50 p.m., FDNY Battalion Chief John Rail said.
About 60 firefighters responded and brought the fire under control by 3:20 p.m.
Fire officials believe the blaze started in a closet near the apartment's bathroom, Rail said. The man was found near the apartment's front door.
"We forced open the door, [and] he was right out front," Rail said.
The man was taken to Beth Israel Hospital in critical condition, the FDNY said.
A firefighter suffered minor injuries as well.
Fire officials were still investigating the fire's cause Wednesday afternoon, but it appeared to be electrical, Rail said.