Lindt Cafe - Martin Place Sydney is Under Siege (Dec-15-2014)

Hostages have been pressed against the window of the cafe in front of horrified witnesses. Photo: 7News

A siege situation is underway in Sydney's Martin Place as a gunman holds up a Lindt Chocolate Cafe.

Police have confirmed an operation is underway after officers were called to the shop around 9:45am on Monday.

The 7News Sydney newsroom, which faces the cafe under siege, has been evacuated by police.

An Islamic flag - black with white writing on it - has been held up to the glass.

In a chilling drama unfolding in the city centre, Martin Place has been shut down and scores of police are surrounding the cafe.

Trains between Central Station and Bondi Junction station has been stopped while buses are now being diverted away from the area.

Reference: News7