Three British teenagers are believed to be on their way to Syria, lured by militants from the self-declared Islamic State.
Scotland Yard has issued an urgent appeal for any clues that may lead to the whereabouts of the school girls, because police say if they make it to Syria, they may never be able to return.
"We are extremely concerned for the safety of these young girls and would urge anyone with information to come forward and speak to police," Counter Terrorism Command Commander Richard Walton said in a statement. "Our priority is the safe return of these girls to their families."
Scotland Yard says that Shamima Begum, 15; Kadiza Sultana, 16; and a third 16-year-old girl who police are not identifying left their home on Tuesday before 8 a.m.
Police say the three friends gave their parents a "plausible reason" as to why they would be out Tuesday. The girls then headed to Gatwick Airport, where they boarded a Turkish Airlines flight.
The BBC reports that the case has already sparked discussion about how these girls could be moved to leave their families and join extremist organizations. The network adds:
"Home Secretary Teresa May said it was important 'to look at the whole question of the ideology that is driving these actions.'
" 'We're very clear as a government that we need to look at extremism across the whole spectrum and that's why we're working on an extremism strategy.'
"Salman Farsi, a spokesman for the East London Mosque, said she thought the girls had been misled.
" 'I do not know what was promised to them. It is just sad. I think the girls need to know they have done nothing wrong. They have been manipulated.' "
This case echoes the case from Colorado, where three teenagers from the Denver suburbs left home with plans to join the Islamic State. The girls in that case were intercepted by authorities in Frankfurt, Germany.