The two surviving Americans were in stable condition, according to officials.
"They are conscious, and have been able to talk to doctors," said Juan Carlos Poli, a city hall spokesman in the Pacific port city of Arica. "The main concern is because of their age."
The tourists were returning to Celebrity Cruises' ship Millennium from an excursion to Lauca National Park when the bus plunged off the rugged highway Wednesday near Arica, 1,250 miles north of Santiago, he said.
Poli said the bus, which had a capacity of 16 passengers, "was totally destroyed."
Celebrity Cruises President Dan Hanrahan told reporters in Miami that the victims were part of a B'Nai Brith group. He said the company was flying some relatives of the victims, as well as company officials, to the scene.
He also said that the bus tour was not among those the cruise line offered to its passengers and Chilean officials said the bus was not authorized to carry passengers.
The bus "was not registered with the Transportation Ministry," said Jorge Caceres, head of the ministry's office in the region where the accident occurred.
Pedro Mufeler, regional director of the government tourism agency, told the Associated Press by telephone that the small company, named Andinotours, had filed its request for registration some 15 days ago but it had not been approved yet.
Two Chileans — the driver and the tour guide — were also hospitalized, but Poli said they were in better conditions and the guide was expected to be released Thursday.
He said doctors performed autopsies of six of the victims during the night and the remaining six were expected to be completed shortly, so the bodies can be sent home as soon as possible.
Celebrity Cruises has established toll-free telephone lines for family members of guests on the cruise. The number is for family members only. Callers in North America should dial 1-888-829-4050.
U.S. Embassy spokesman John Vance said the embassy was sending consular officers to Arica.
Hanrahan said the victims did not make the reservations for the bus trip through his company, and said Celebrity did not know the bus operator. "We have not worked with this operation before," he said.