Joe Sestak, a former Pennsylvania congressman and retired Navy admiral who is president of First Global, the nonprofit group that organized the competition, made the initial call to the police shortly after midnight, officials said. The authorities began sharing photographs and descriptions of the teenagers on missing persons fliers on Wednesday.

The police searched Constitution Hall, interviewed other competitors in the dorms and unsuccessfully tried to reach one of the missing students uncles, according to police reports.

The teenagers all have one-year visas, officials say.

The Burundi Embassy in Washington said in an email that officials there had not known there was a team from their country in the United States until after the teenagers were reported missing.

In June, the State Department issued a travel warning for Americans going to Burundi, located between Rwanda and Tanzania, citing political tensions, political and criminal violence, and the potential for civil unrest. The warning took note of a tenuous political situation and reported ambushes and kidnappings.

More than 325,000 Burundians have fled the country since 2015, mostly to Tanzania, Rwanda, Uganda and the Democratic Republic of Congo, according to Human Rights Watch.

The First Global competition made international headlines after the all-girl team from Afghanistan struggled to get visas to attend the event, advertised as an international robotics Olympics. Students from more than 150 countries participated in the competition, organizers said. It is scheduled to take place in Mexico City next year.

First Global is always concerned about the safety of our students, said Jose P. Escotto, the organizations communications director. The group said it had advised students not to leave the dorms or Constitution Hall without a mentor.

Students and their mentors stayed in dorms at George Washington University and Trinity Washington University. The Burundi team stayed at Trinity Washington University in Cuvilly Hall, a university spokeswoman, Ann Pauley, confirmed in an email; the hall is locked at all times. First Global provided bus transportation between the dorm and Constitution Hall.

Members of the Norwegian team, waiting to leave for the airport Thursday morning outside Thurston Hall at George Washington University, had heard about the disappearance from another team but thought it was a misunderstanding.

They havent been found? asked Havard Krogstie, 17, from Trondheim. I thought it was just they had gone somewhere without telling anyone. I dont see why they would just run off in a foreign country.

Right now, he added, with a shake of his head, I realize that theyre actually missing.

A version of this article appears in print on July 21, 2017, on Page A12 of the New York edition with the headline: 6 African Teenagers Disappear After Robotics Contest.

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Burundi Robotics Team Vanishes After US Competition - New York Times