-- At least 12 people were killed, including five Americans, after the bus they were riding in Tuesday was involved in a crash in Mexico, an official familiar with the investigation told ABC News.
The passengers involved in the crash had been traveling on two Royal Caribbean cruise ships, a spokesman for the cruise line told ABC News.
Four of the other fatalities were Canadian, two were Swedes, and one was Mexican, the official.
One of the fatalities was a minor, according to the Quintana Roo government. The minor's nationality is not yet known.
The tour bus crashed in the southeastern part of the Yucatan Peninsula on Tuesday shortly before 10 a.m. local time, according to a spokesperson for the attorney general's office in the Mexican state of Quintana Roo.
The passengers aboard the bus were American, Italian, Swedish and Brazilian, according to a statement from the Costa Maya port, which is near the crash site. The bus belonged to the port and crashed at kilometer 5 of the Mahahual-Cafetal highway, the statement said. Emergency services and medics arrived on the scene immediately after the crash, the state government said in a statement.
The bus was seen overturned on its side, and multiple passengers were seen lying and standing on the side of the road in video filmed at the scene of the crash.
Vítor Maciel Fontes Jacques, 32, from Brazil, was traveling with his wife and five family members when the bus crashed. He suffered a broken clavicle in the accident while his sister-in-law suffered a head injury that required surgery, he said.
"The bus somehow went down the side of the road," Fontes Jacques said. "Then the driver pushed it over and it started flipping over. And then the bus flipped on its side."
The tour bus in the crash was carrying guests from Royal Caribbean's Celebrity Equinox and Serenade of the Seas, said cruise spokesman Owen Torres.
"The news from Costa Maya about a bus accident involving our guests is heartbreaking," he said. "Our hearts go out to all those involved. We are doing all we can to care for our guests, including assisting with medical care and transportation."
The cruise line is in contact with local authorities, Torres said.
Royal Caribbean tweeted that it had 27 guests aboard the bus, which was headed toward the Chacchoben Maya ruins, about 110 miles south of Tulum. According to the Quintana Roo government, 31 people were on board the bus. A tour guide and driver were among those on board, the port said in a statement.
Carrie Vanrenterghem, who traveled with her two daughters to the same excursion on a bus directly in front of the one that crashed, said she saw the bus being towed away on their way back from the Mayan ruins.
"We didn't understand or know what it was," the Oregon resident told ABC News during a FaceTime call after she arrived back on the cruise ship.
Vanrenterghem said that one of the sides of the bus was "smashed" after it fell on its side and that the "whole windshield was gone."
"You could tell that somebody had probably gone ... through the windshield," she said, describing the scene as a "hard" sight to see.
"The seat belts were tied below the seats, so no one told us to put the seat belts on," Fontes Jacques said. "But my wife’s sister saw them and she asked us to put it on. Her sister did take it off later. I put it on, but I took it off later. And we were the two of us hurt a little. So that’s the lesson of the day, to always wear a seat belt."
Vanrenterghem said that had she and her daughters booked their excursion through the cruise line instead of an outside travel agency, they could have "easily" been on the bus that crashed, along with their fellow cruise passengers.
"Most likely, we would have been on that bus," Vanrenterghem said, adding that the close call made her "realize that life is short and family is important."
The Celebrity Equinox is on a seven-night cruise that departed from Miami on Saturday and had scheduled stops in Key West, Florida; Costa Maya and Cozumel, Mexico; and George Town and Grand Cayman in the Bahamas, according to Royal Caribbean. The Serenade of the Seas departed from Fort Lauderdale, Florida, on Friday, with stops in Key West; Roatan, Honduras; Costa Maya; and Cozumel.
During a briefing Tuesday afternoon, U.S. Department of State spokeswoman Heather Nauert said officials were following the news of the bus crash "very closely" and described it as "certainly a tragedy."
Mission staff from the U.S. were en route to Mexico Tuesday to assess the situation, she said.
ABC News' Conor Finnegan, Ben Gittleson and Scott Withers contributed to this report.