NEW YORK — A 19-year-old student who fell from the second floor of a New York University dormitory and spent a day and a half trapped in a narrow shaft between two buildings is in good spirits, despite suffering several broken bones, relatives said Monday.

University officials and city police were still trying to figure out exactly how Asher Vongtau happened to tumble into the shaft, which is less than 24 inches wide and sits between a NYU dorm and an adjoining condominium building and parking garage.

Vongtau’s friends said they noticed him missing at around 7 a.m. Saturday. By late morning, they were posting messages on Facebook, asking if anyone knew where he was. His whereabouts were a mystery until late Sunday afternoon, when a campus safety officer spotted the missing student’s mobile phone on a fire landing at the rear of the building, then heard Vongtau moaning.

Firefighters broke through two cinder-block walls to reach him.

Vongtau’s mother, Habiba Vongtau of Pittsburgh, told WABC-TV her son suffered a broken arm and a cracked pelvis in the fall, among other injuries. He was being treated at Bellevue Hospital.

“He really can’t remember up until when he fell in there, exactly what happened, maybe as he comes to,” said Vongtau, who didn’t return phone messages from The Associated Press.

Police said Vongtau, who did not live in the dorm, told investigators he had been at a party and was leaving early Saturday when he lost his footing and slipped while going down a stairwell.

The student’s sister and father both posted on Twitter on Monday that he was doing OK.

“Spoke to Asher, he’s in good spirits,” his father, Lulufa Vongtau, wrote. “His mother and I are grateful to God for this gift!”

NYU spokesman John Beckman said the school was grateful he wasn’t more seriously injured.

“We believe that we can learn something from every incident, even ones that have a happy ending, and so our Public Safety Department will be reviewing what happened here with an eye toward what, if any, lessons should be incorporated for our response to missing person reports going forward,” he said.