Update at 12:17 a.m. ET
An undisclosed number of hostages are being held at a chocolate shop and cafe in Sydney, Australia.
As The Associated Press reported earlier in the day, TV footage had shown individuals holding their hands up against the window, as well as "what appeared to be a black flag with white Arabic writing on it."
"We don't yet know if this is politically motivated, although there are some indications that it might be," Australian Prime Minister Tony Abbott said of the situation, according to Reuters.
Nearby offices have been evacuated, and police have sealed off Martin Place, the central business district where the Lindt cafe is located.
The United States has evacuated its consulate in the city and issued an warning to Americans in Sydney, Reuters reports.
Events are still unfolding; we'll update this post as news comes in.