PORT-AU-PRINCE, Haiti — An hour before the earthquake struck, 19-year-old Britney Gengel phoned her mother in Massachusetts, bursting with joy: She had found her calling on a college trip to help orphans in Haiti.

Now, as recovery crews continue to scour the collapsed Hotel Montana where Britney and 14 other Americans are believed buried in the rubble, Len and Cherylann Gengel are waiting with dread for another call — this time confirming their daughter's fate.

"It is a living hell on Earth to be in this limbo," Len Gengel said.

Gengel's daughter and three other students from Lynn University in Boca Raton, Fla., are believed to have been trapped inside the Montana when the Jan. 12 quake struck, turning the six-story landmark into a tangle of broken concrete in the flash of an eye. Some 100 people are believed buried there.

The U.S. is pursuing the cases of about 4,000 Americans unaccounted for in Haiti, according to State Department spokesman Noel Clay. He said that number could drop dramatically because many are Haitians with U.S. citizenship who travel frequently between the two countries and are more difficult to track. So far, the U.S. has confirmed 79 American deaths.

"The departments of state, defense and health and human services are working together to recover, identify and repatriate remains of American citizens in the absence of functioning local mortuaries and commercial flights out of Haiti," said David Searby, a spokesman at the U.S. Embassy.