The team, consisting of two 17-year-old girls and four boys, aged 16 to 18, was reported missing after the competition's closing ceremony in Washington on Tuesday night. They were last seen in the area of the D.A.R. Constitution Hall near the White House.
Washington, D.C.'s Metropolitan Police Department reported on Thursday that two of the teens had crossed the border safely into Canada. It's unclear how and when the students got there, what they were doing there, and where the other students are, according to police.
There is no indication of foul play in the disappearances, police added in the statement.
Canadian authorities could not confirm the entry of the two Burundian teens, telling ABC News, "It is not a practice of the Canada Border Services Agency to confirm and/or deny the entry of any one person to Canada."
The robotics competition grabbed headlines worldwide after an all-girl team from Afghanistan was twice denied U.S. visas to compete, but the White House later intervened in a last-minute act, granting that team and its chaperone a special parole to enter the country on a short-term basis.
The president of FIRST Global, the organization that runs the competition, made the initial call to the police about the missing team and has been assisting authorities, according to the group.
"Security of the students is of paramount importance to FIRST Global," they said in a statement, adding that students are "always to be under close supervision of their adult mentor and are advised not to leave the premises unaccompanied by the mentor."
The Burundian embassy in Washington did not answer multiple phone calls or respond to an email from ABC News.
Burundi is a small, landlocked country in Africa's Great Lakes region, bordering Rwanda, Tanzania, and the Democratic Republic of Congo. The State Department issued a travel warning on June 23 for the country, noting, "The political situation in Burundi is tenuous, and there is sporadic violence throughout the country" after President Pierre Nkurunziza ran for and won a controversial third term in 2015.
In the aftermath of that election, state security forces have conducted numerous killings, disappearances, abductions, torture, rape, and arbitrary arrests, according to Human Rights Watch (HRW), with attacks and killings by armed opposition groups as well. More than 325,000 Burundians have fled the country since 2015, according to HRW.
Burundi has a high refusal rate for business and tourism visa applications, with 61 percent of applicants denied -- an indication of U.S. authorities' fear that someone might overstay their visas and remain in the U.S. illegally.
ABC News's Ely Brown, Dee Carden, and Ben Gittleson contributed to this report.