A North Korean defector was believed to be holed up Thursday inside the South Korean consulate in Hong Kong seeking refuge, news reports said.
The consulate was under tight security and journalists were being told that officials would not comment on the matter.
The teenager was thought to have been in Hong Kong for the International Mathematical Olympiad, which was held at a local university earlier in July, the South China Morning Post reported.
In the early 2000s, many North Koreans sought asylum at foreign embassies, but the number of defectors has dropped in recent years.
Most do not normally seek passage through China, as Beijing forcibly repatriates would-be defectors to North Korea.
Hong Kong has a separate legal and governance system to the mainland, as part of the Sino-British joint declaration.
North Koreans have been visiting, living and studying in Hong Kong since the territory's handover to China in 1997.
Several North Koreans have studied at the University of Hong Kong. The nephew of current leader Kim Jong Un reportedly wanted to study at a boarding school in Hong Kong but was denied a visa.